Are you able to orgasm by masturbating?? If so, it may just be because you are nervous with her. As far as the tiredness, it could be from holding yourself up, maybe try some different positions?? If not, you may want to get checked out by a physician.
You just need a good position and to be at the right angel when you do it. Make sure you're comfortable before you start. If you feel tired then you are probably doing it wrong. google for "sex positions", watch some porn and learn (not the freaky stuff) As for not being able to cum, It could be because you are working too hard because you're not comfortable in the position. other reason I can think of right now is - you are just doing it too slow. When you find the right angel and you're comfortable with it try to speed up, that will make the cum come quickly.
Yeah, being comfortable has alot to do with being able to orgasm. Also, the pressure and exccitement of the first few times can make it difficult. On the plus side, you aren't blowing your load when she looks at you, which is what I did the first time. Try different positions. Spooning on my side is the go too position whenever, I'm physically exhausted from the gym. Sex is a workout, so make sure you're in shape. Cheers
