I thought I was maybe pregnant so I went and got a test done at family planning but it was negative. I haven't missed a period but my last one was only 2-3 days when usually it's a week. I get headaches, cramps, gained weight, I don't eat a lot, urinate more often and usually I feel sick. Could I actually be pregnant or could it just be in my head?

Chances is you are not pregnant if you got a negative test AND you had a period. While you only bled for 2 - 3 days, every once in a while we women have a strange period, whether it be shorter... longer... late... or early, it does happen.

The symptoms you describe could be due to a number of different things other than just pregnancy. Unfortunately you are now going to have to wait to see if you do in fact miss your period.