My periods are usually very very light and last about 3-4 days. 2 1/2 months ago i had a very heavy period that lasted 16 days. I’m on birth control so i skipped my last 2 periods and decided to take the sugar pills for this month. My period lasted for half a day and hasn’t come back and was very light. I’ve taken 4 pregnancy tests all are negative so what could this be??