I think you where good at the start compensating your lack of skill with burning desire and faster movments. Whats your penis size? I hear if its too small than you cant satisfy women. Next time when you have sex pay attention maybe it doesnt even touch the sides.
Anyway some women are not into sex at all. Some even ask for intercourse while in fact guy is already in them - just cant feel it even with average dicks.(look in yahoo answeers) Anyway you should talk it over what the heck is she thinking about it and how she feels. Express yourself to her too.
Doubt kills more dreams than failure ever will