Not sure if this would help, I think it may have in my old relationship where it hurt my ex, not because I was going too deep, just the angle was painful. Try google for perenium massage. Erm, better yet, I'll do it.
http://pregnancy.about.com/cs/episio...erimassage.htm
I forgot where I saw a thread about this, it may have been on here or askmetafilter, but try it out and see if it helps.