Could I be pregnant and not know it?

First off I have never had a normal menstrual cycle so I never know when I'm ovulating. I have been spotting since May and my last semi-normal period was in April. For about 2 or 3 weeks now I have been craving pineapple and I'm not much for it, I'd eat it once in a blue moon, but now I want it all the time. My stomach is hard on the upper half and I naturally have a big tummy cause I'm over weight. My stomach keeps hurting and once in awhile I keep feeling like I'm gonna get sick, but never do. I also am hot where ever I go or am (even in air conditioned rooms) and I know it's hot out, but I can't ever get to be not hot. I have been taking pregnancy tests for a while now since I got married in May, but they all turn out negative. Could I be pregnant and not know it? Could the tests be wrong?