Hi, me and my boyfriend had this problem for a while when we first got together. The way I got over it was by, as NOHARD said, I got on top of him and took the control, it still hurt at first and we did have to use lube for a while but it really helped me relax knowing that I was in control.
I would advise you to go to your doctor though, a lot of women do have these kinds of problems. I know it's hard but try not to worry too much about this, I'm sure you'll get it sorted.
Good luck.
Hi Cr, I think your find that your having vaginal spasms, for you relaxation is the name of the game, have a look on dodson and ross, you can googlr that it will take you there, down the left hand side you will find a section on first time sex, info for you to read, if not you can post Dr Betty Dodson, she may have some advice for you.
As you seem to get this if your b/f is trying to get inside you, reverse the roll, you get on top, by doing this you are in control, and you being in control may stop the spasms, you can go at your own speed, but all the time stay relaxed, see how you go .
Good Luck