Please help!

I have been on BC since I had my daughter 3 years ago. Had sex three times this year with my partner (once in February, then again in March, and again April because our schedules at work were off). Well my periods are all of a sudden changing. My partner used protection when we had sex and I was still on my BC. But my periods went from lasting four days and changing my protection twice a day to now a very very light spotting that would make it where I wouldn't even have to change my protection during my period if I wanted to. It's been that way two months now. I've stopped taking my BC and taken two pregnancy tests but both were negative. I have been nauseous, fatigued, moody, had pelvic cramps, and been gaining weight since April. But I'm confused. What can I do? Am I pregnant? Please help!