I'm 29 and 2.5 years ago I hurt my back due to heavy lifting at work. I get lower back pain and sciatica down my left leg usually, or both legs on bad days. It's especially bad during fall and winter, to the point where doing everyday stuff is either a struggle or outright impossible.
I take it it's likely something I'll have for the rest of my life. I've been to physiotherapy - no results, but I'm still training the way they told me to. Regular painkillers don't help and I only resort to codeine when the pain is a 9/10 because it turns me into a zombie. Usually the pain is a 7/10.
TL;DR: Probably life-long sciatica and lower back pain, not taking any medication for it.
I still want to be sexually active because honestly this is one of the very few enjoyable things in my life at the moment...
Smultron, honey I think you have pretty much covered all the options, do you have any sex position aids to take the strain off your back, have you tried massage as part of your foreplay routine, would you consider acupuncture, do you have a hot tub to use for heating up your muscles. If you can swim add this more into your routine day as this helps my back after a motorbike accident I had many years ago. Bennyboy69 xxx
I agree with BennyBoy about swimming and soaking in warm water. Another suggestion could be an osteopath/ chirpractor depending on who is in your area. My dad has suffered terribly with sciatica and found an osteopath to be the best at helping him. This is just his experience and it's completely your call, but when my dad went to the osteopath, they gave the total opposite advice to what the physiotherapist said. The physio said my dad should take 2 weeks off work to rest, yet the osteopath got him back to work after 3 sessions.
again this was just his experience but it may be useful here :)
Team Fibro here, but I take medication for it which kinda helps.
You've pretty much covered all bases though, just communicate freely, and only so what feels comfortable. Incorporating massage is a good idea, and think about using toys if there are things you want that you can't accomodate the physical position to do.
As long as your partner is respectful, you will be fine.
The most important thing is to not be disheartened, and to continue to be sexually active. DOn't let fear of not being lead you to, well, not be.
Have you tried water?either sex in a bath or oral/manual/toys under hot showers? We can't have full sex in the shower (height difference) and the bath can take some practice but I've found both really helpful. I have constant upper back pain so isolating the part of my body that exacerbates the pain helps, so my hands get firmly strapped down. I also find that like all exercise warming up helps, so firm massage with warming oil, some inconspicuous stretches or getting your oh to help stretch during foreplay (after massage my oh will gently pull my hair so I'm curving my head back, stretches my spine and feels sexy at same time lol). You're already doing the most important thing, communicating!
Ciropractor, physio and yoga. Swear to the moon and back by these. I went to the Dr at 24 woth chronic back pains, couldn't straighten up etc, got sent for xrays and when i got my results i walked back into said drs and he laughed and told me he'd just had a 50year old in with a better back than me. I got sent to a physio and that worked, booked myself into a ciropractor and another physio through my rugby club and I've noticed my back is 10000 times better than it's ever been. Recently I started yoga to open it and stretch it out and again, the difference is uncanny
Thank you all so much for your replies!  Quite a few unplanned stuff came up, so I read them quickly but didn't have time to reply until now.
Bennyboy69 I'm planning to get more sex position aids, but atm the only thing I have is a 'bolster' (not sure if this is the right word for it). It's rectangular, stiff and big so that my legs rest at a 90 degree angle when I'm lying on my back. During sex I can lean over it for doggy style. I have a hard time relaxing to receive a massage, but I will give it a few tries when I get the chance to. Nor have I tried acupuncture, but I will ask my physical therapist about it when I see him again in September. Applying heat offers little to no temporary relief and causes me more pain afterwards, even though I keep myself warm. Swimming is unfortunately not an option, as the nearest pool is too far away, but I'm glad that swimming helps you!
MGB93 I've seen a chirpractor twice (that's what he thought I needed) but I didn't see any change. It's really expensive, so it doesn't feel worth insisting I visit him more 'just in case it helps'. :(
PrincessSparkle yes, using toys really helps! I'm also trying new, more simple positions to see if they work. Thank you for the encouragement! 
Guy14357 that's interesting! I suspect it might be the endorphins / dopamine. ;) Tying me down is a big no-no as it can cause cramps, and when I'm having a bad day pain-wise I want to be free to move however I want whenever I want.
Foxiiuk I haven't tried anything with water in many years because I hate how it removes all (natural) lubrication. I can give it a try with some silicone lube, though! I can't think of a way to make anything sexy out of the kind of stretches I was shown by the physical therapist, but I can send my partner to take a shower or something, so I can do them on my own without ruining the mood.
Bigiain, I'm seeing a physiotherapist and have been to a chiropractor twice as he advices, but saw no results. If my back gets better, yoga is definitely on my to-do list!
Hi smutron I’ve also had a bad back for the last four months I did visit a chiropractor 4 times gave me some relief not much . Also had a couple of sport massages again gave small relief for a couple of days . I have recently seen a osteopath now had 2 visits I finally feel a lot better and on the mend can’t recommend osteopath enough hope you feel better soon
I see an osteopath regularly. As soon as I feel that twinge I book in or am locked solid for a week. If you know your triggers you can help yourself a lot.
I use pillows to help me get in position and stay there (little use of my right leg).
Exercises like yoga stretches done regularly are helpful. I also have fibro so finding the energy to do them is a problem in itself. I'm the first to admit I'd be a lot better if I did do them more often.
My sex drive is still alive and kicking though, so with a little help from some purchases from Lovehoney and a lot of help from my OH, at least I can still manage to get a lot of pleasure in bed 
well a coupleof years ago i was going thru the samething my doctor said it was a disc bulgeing sowe did an mri and i had 2 L5 S1 insurance would not pay for S1 so its still bulgeing he fixed L5. Eveytime iwent to see him before surgery he asked if i was going to the bathroom ok not thinking i said yeah. well my uroligist kept saying i was retaning a lot of pee just thought old age right. well after my back surgety i went to the pee dr again he says your bladder is empty thats when i told him about my back surgrery he ok that explains it . they say if i would have not had surgery i could have a lot in that part of the body so go get it fixed and go on with life taking pain pills will do damage also to your colon. surgery isnt that bad just follow dr's orders.