What is my body doing??

So for the last 2 months AF has been a week early, extremely light and only lasted 2-3 days which is unusual. I'm usually right on time, lasting for 4 days and heavy on the two middle days. I've been extremely moody, boobs have been sore and randomly nauseous. I thought maybe this meant I was pregnant but I've taken 3 tests and they've ALL been negative!! Now for the past two days I've had slightly awkward pains in my lower belly. Can anybody help me out and tell me what's going on with my body?!?