What Causes Heavy Periods With Cramps And Vomiting Sensations?

This month my period was really odd. I am on the pill and I started my sugar pills on Sunday normally I start my period by Wednesday but this month I didn't even start spotting until Friday and it was really light and pinkish. And I've been feeling sick to my stomach all week and haven't felt good. Today my period is heavier than normal and I am having really bad cramps that come off and on followed by feeling like I need to throw up. I could have gotten pregnant this month because I was on antibiotics and I did miss a few pills but took them the next day. But I took a test and it said that I wasn't.