Extreme Vaginal Discomfort after Sex

My girlfriend and I have been together for 2 years now. She's on the pill and we have unprotected sex every time with lube (ky). My penis is big but not huge (7.5 inches) and every time we have sex she experienced extreme discomfort and usually bleeds after sex. She has switched her birth control twice now and has gone to the doctor and all she has told her is that she has a very small vaginal canal or something along those lines and she has had no relief. This is destroying our relationship. She now has no sex drive at all, she fears having sex just because of how extreme the pain is after. Please help us.