You are in Living Better . Sizing up the Problem Painful intercourse, or 'dyspareunia,' is a surprisingly common condition that affects up to one-third of women at some point in their lives. In any case, intercourse is sometimes painful for her and less fun for me. Let me put your mind at ease. Although we hear a great deal of talk about penis size, the reality is that most of the difference only exists between flaccid penises.
Vaginas are highly elastic, and most can accommodate almost any size penis.
Without knowing more specifics, I can't know for sure, but I can think of some possibilities and suggestions. It might be that you are not giving her enough time to become aroused before beginning intercourse. Be sure to engage in lots of foreplay. Try using a lubricant. Changing position might be helpful.