I had the same problem....I was too STRESSED so my muscles TIGHTENED...it can be solved by practicing inserting your finger into your vagina, it is YOURSELF so your muscles will be RELAXED, practice, practice, until you get used to the feeling of a presence there..then, you will find visualizing this feeling of relaxed-ness, keeping relaxed muscle wise, it will not hurt nearly as much if at all....

.......................................this worked for me, I read it in Sex For Dummies!