What Causes Nausea, Headaches During Menstrual Cycle?

Hi for the pass two weeks I have had nausea, headaches, feeling like i'm going to throw up, but didn't. pain in my abs and rib cage. My body was bloaded, breast got bigger, my periods were one to two days late, so I took a pregnancy test and it was negative. Today I got my periods, but its light with blood clots. I also feel light headed and cramping, and im not as bloaded as before, whats going on ?