He's having problems keeping an erection and were in our 20's... Is this kinda normal....

Hello everyone, kinda a touchy subject but my husband to be has problems keeping an erection sometimes. He was a virgin up until a year ago, we are both 24. He has ADD and we think that is the problem and everytime we say anything to the doctor they say he is to young to be experiencing this. They blame it on his ADD. He can not take medication for this because nothing works without bad side affects. I was wondering if anyone else's partner has this problem? If so does anyone have any advice?