....i'd say nervousness...i had that problem too......what i would consider a hot ass girl (i like goth/headbangers....alot of people say they're disgusting but that's the hottest woman for me) and i coudln't keep it up.....not for shit...i had one drink of wine and other than that no other drugs whatsoever in me at the time.....not even left overs....but i was nervous so i'd say it's that for you too.....