on August 26 me and my gf had sex for the first time and we were being extremely safe. We changed condoms multiple times when we did it. I did not cum at all but she thinks she is pregnant because she said her breasts feel bigger and a little sore. and I want to know how much of a chance is there of her actually being pregnant? And if not then what can explain her breasts feling a little bigger and a little sore? Please explain...