what could this be?

alright can y'all help me out? my body has been confusing the crap out of me. okay so January my period was 10 days late and was really light, spotting for 5 days and one day of light bleeding. February it was 5 days late. so technically I didn't have a period for February. April 1st my I had another period. three days early. well throughout this whole time I noticed my lower abdomen getting a little bigger and it feels harder. I also I'm hungry a lot. and been having nausea randomly. and very moody. I can't suck my tummy in anymore other wise it is extremely uncomfortable. so I just want to know what could be happening. I want to be pregnant but I can't be. all test I have taken the last three months was negative. it wouldn't be because I'm stressed have been less stressed the last 4 months then my whole life. I don't think it's a chemical one because I know im pregnant obviously from the test. I just want to know what could be happening. anyways sorry for the long rant. thanks girls.