help with inserting long toys in the anal area

i use large toys and butt plugs on my bf and he can take them but once he just gets a few inches inside we have to stop as he gets pains in hes stomach but its only after about 3 or 4 inches inside,is there a reason for this or maybe im doing it in wrong position,iv tried doggy and on hes back but still same problem any help be good

Firstly, it may be a good idea for him to get a check out by the doctor just to make sure everythings okay back there because you never know. =)

Otherwise, this thread may be helpful. http://www.lovehoney.co.uk/community/forums/sex-tips-and-talk/383783-how-to-take-more-length-during-anal/