3 Weeks ago a friend and i had anal sex. He didn't use a condom, but he stayed strictly in my ass. Before we even got to that though, he did finger my vagina, then my ass, then back to my vagina, and then we had anal. When it came time for him to ejaculate, he came inside me (my ass). Its been almost 3 and a half weeks since then, and I've gotten my premenstrual cramps and sore breasts but no period. Not to mention I've been under some moderate/heavy stress with dealing with my end of course tests, but now I'm just waiting for my period to come along. I have also been on some new antibiotics for a sinus infection, and i heard medication can sometimes mess up your cycle. It doesn't help that my cycle is also very irregular. For the last two months, my period came around the same days, but ever since before that, it just started when it wanted to. I'm planning on taking a pregnancy test next week if i don't get it by then. So tell me, am i just paranoid or possibly pregnant?