Whilst I can't advise you on any medical remedies and have no experience in how the problem may be "solved" I would recommend a couple of techniques to "dealing" with it should it persist unsolved (or even if not, these are good sexual practises anyway):
1) Sex is not just penetration - he can pleasure you orally, manually and using toys and you can do the same for him.
2) Soft blowjobs are (apparently) bloody wonderful! So make the most of his softness and give him lots of oral pleasure
3) I do believe men *can* orgasm without an erection too!
So really, I'd focus on him feeling more confident and comfortable gaining pleasure from your sex lives - spend time finding *new* ways to enjoy sex and hopefully you will both feel really fulfilled.
Penetration should (IMO) be something you focus on later down the line - focus on general pleasure, then look up how to restore his erection - definitely speak to your doctor or a sex therapist for tips! I'd not bother with herbal remedies - they often don't work - so see your doctor, if any herbal remedies *do* work - the doc will know about it and be able to advise you safely (some herbal remedies can be quite dangerous if taken in the wrong way).
I have managed penetrative sex only a handful of times in 2011 and I would still say I have a healthy, happy sex life and my OH would certainly agree - definitely work on a positive mindset and you can deal with anything! Don't give up on the erection front, but in the meantime, try and enjoy sex as things are :)