Perhaps you're overtrained or you may have conditioned yourself incorrectly. How exactly were you performing your sessions?
Two hours of any stamina is an enormous strain to put on your member.
Umm..I just slowly jerked it (or quickly sometimes) till i felt like i was getting close then i backed off till the feeling left then i did that over and over again... then when i feel like it I let myself go...
Two hours was my max time i made it too usually i didnt have 2 hours to spare..