I Have My Tubes Tied Since 2005. My Periods Are

I have my tubes tied since 2005. My periods are very abnormal. light spotty, no cramps , no clots , nothing as a symptom of my period but i gained weight . in two weeks i gained 16lbs. I have plenty of symptoms of a pregnancy but negative hpts. my belly is really round more firm on the top than on the bottom by my pelvis. what could this be?