well i dont know about some girls but after 2 hrs i would just give up...lol.
sometimes i can orgasm real quick and sometimes i just cant no matter what i or my b/f does. 2 hours of sex i would just be sore and worn out.
if you feel like you are getting close, pull out and try doing some other stuff to her like oral, or get a dildo or something to keep her going, then when she starts to get real close you can jump back in.
hope this helps
oh and as far as the pain, i can only guess its from having an intense erection for over 2 hrs.