Im 19 years old and I have had alot of sex before in my past..I used to be able to have sex for hours and hours everyday and I could get hard really easy..but the past 5 or 6 months its like I can't even get it up..I'm experienced, and I have been having sex since I was 16 so its not like im nervous or anything..I just don't understand..I get hard when I am masterbating..But when im with my girlfriend the only way I can get hard is from oral pleasure..and most of the time it becomes soft before I can get it in for intercourse..I don't take any drugs or prescriptions medicines..And im in great shape...So I don't understand what is wrong..I used to take 17hd..It was a weightlifting supplement..I don't know if its a coincidence or not..but after I took that is when I started having this problem..