Am I pregnant?

Hi everyone,

I'm 19. Lately I've been feeling really tired and often get short cramps lower down in my belly. I stopped the pill half a year ago because I was on a different pill that didn't mix well with it, but after I stopped the pill I had unprotected sex with my partner. I didn't get my period last December, nor in January 2014. I did get it in February, but it was way too early. In March I got my period twice (or bleeding) – one period lasted 3-4 days and then another lasted a week. I've done 3 pregnancy tests (2 in December and 1 in January), all negative. Still, I get headaches, I'm often tired, sometimes feel lightheaded, eat more and have gained weight (that could be because of eating more). During sex I sometimes have mild pain in my lower belly. Lately I've also had shaky legs, a gurgling stomach, and light pushes in my belly, but those go away quickly.

Am I pregnant after all, or does anyone know of something else that could cause these symptoms?

HELP, thanks in advance!