I had unprotected sex a day after my period finished 3 weeks ago, he didn't come inside me but all over me. Since then I have been feeling really down, I'm always really tired and when I get up I feel dizzy and my legs feel like jelly. I feel like I'm going to throw up but I haven't yet. I have lost my appetite and I've been having really bad cramps and headaches. Also my lower back is killing me. I've got this gut instinct that pregnant but people keep telling me that I can't fall pregnant a day after my period. My period isn't due for a few days, but I've never really had pms before. Could I be pregnant?