I had sex on the 26th of December and we used a condom, but it kind of slid off. Anyways, now I have been sleeping a lot more and I have been taking a lot of naps, feeling nauseous, and a lot of cramping. I thought I had my period 2 weeks ago, but now that I think back on it, it was light and short (not my normal). I took a pregnancy test and it was negative, but maybe I used it wrong?? I don't know. I am going to take another one, I just don't know when.