are we pregnant

my girlfriend and I are wondering if she is really pregenant or not. We had sex three weeks ago without a condom and I pulled out even before I felt anything. However on the Friday the 9th she said her breasts hurt and she was cramping. She started her period the very next day but her breasts have never hurt before her period and her blood wasn't brown and was flowing normally. She also has been off her patch. We had sex again on the 14th which was valentines day but used a condom which didn't break. However she has been feeling these pains still on and off. On the 18th she said she felt nausau and the cramps. So that day we took a home test which came back negative. Today 19th though she said she felt fine so she put back on her birth control. This afternoon however she felt the cramping again which she said was a little worse so much when she sat down she felt better. She does also feel like she is gaining weight and has been eating more than normal. Her stomach has been the only thing hurting so far but it's above the naval not below. She has been more tired than usual but not fatigued. We are going to the doctor on Wed and are hoping she is not; seeing we both only work part time and have no place of our own. Also I'm in college know and she starts next August. So I'm asking you is she pregenant or is it something else?