have you ever tried a 2nd round?
I've been with 4 men and 3 of them came really fast the first time we were together. two of those were so embarrassed that it stopped there but the third, and current, went again and man, he went all night.
it could also have to do with who your sleeping with. if you are with one girl that loves you and accepts you just relax and keep trying. if nothing else the routine of it should eventually lengthen your time
of course I am a girl so I could be wrong.