My girlfriend and I have sex, but I can only enter her vagina when her legs are nearly closed - missionary and spooning from behind. When her legs are spread or she's on top I can't get in... is this just how she is? That's ok with me but if we could try more than two positions that would really be fantastic. Maybe there are some exercises or something?
The fact that you can penetrate in several positions makes me wonder if she has some emotional concerns about the other positions, such as is she anxious (for whatever reason), anticipating pain from those positions, or other thoughts that are interfering with her arousal. For example, the woman on top can be a more intimate position because the two partners can not only make eye contact, but she can also see you looking at her body. If she has any negative thoughts about her body image, this could interfere with your ability to penetrate her.
There may be another reason that I'm not thinking of that's causing your difficulty, but at least this gives you a starting point. Perhaps you need to spend more time getting her aroused, which might allow you to penetrate in the other positions.
Perhaps you can probe gently as to her thoughts about having intercourse in these other positions with you.
I hope that gets you started.
Jennifer L. Fee, Psy.D.
The Stress Masters