You probably aren't pregnant. A little bit of ejaculation or a lot.....you can get pregnant from either. If you take your BC religiously and took a morning after pill, what you are feeling is most likely a "flu" like you think it is. Cramping can be from the flu, pill, food allergies, or PMS or even from having sex.
Take a bit to relax and stop being so scared, because I think you are ok.