Difference's in pregnancy, and pms. Pms?

Hello, my girlfriend is on birth control, bust does not take is at the same time every day. Sometimes fluctuating as much as 12 hrs, but anytime she notices she misses she takes two to make it up. Last week (5 nights ago) we had sex for the first time. I believe that I pulled out in plenty of time, however there was fluid that I assumed was pre cum that could have got on the exterior of the vagina. I never lost an erection, and didnt climax, however this fluid did smell like semen does. I know that some precum can contain sperm, and I'm not sure whether it is possible to release actual semen without climaxing and losing an erection. Anyways, that was 5 nights ago, my girlfriend took her last birth control pill last night(4 nights after we had sex) She had begun to feel cramps slightly before she took her last pill, and felt them again today. She said that they appear when we kiss or she is arroused. Could these cramps be from implantation, or are they just pms?