look at it this way, the opposite could be a problem.......me and my girlfriend have screwed for 2, sometimes 3 straight hours, different positions, different holes, etc etc, but to the point neither one of us could move the next day.........
then other times we've gone for just 20 minutes or so.
here's what you need to do. you need to masturbate. and i mean, get yourself to the point of no return, and STOP. don't cum. wait a second, and do it again. keep doing it till you can pinpoint the exact point you need to stop. keep doing it, keep stopping.
do that for a whole hour, till your penis head, the most sensitive area is red sore. then rest a couple days. and do it again. cycle it.
you can teach your body to control the point of no return better, and when the rawness heals, your sensitivity lessens. but you need to do this regularily till you can master it.
new years eve, after being out a bit and a couple shotys of petron, (always gets her naked) we started screwing at 11 pm and our excellent sex lasted till 1:15 am! it was HOT and intense and the speeds and intensity changed constantly.
of course, once she starts squirting, it's tough NOT to cum, but it takes practice.
good luck.