i have been taking birth control since december, in june i missed three days of birth control pills, and then the first week of july i got a very mild and short period. then about two weeks later i got my period again, only this time it was a heavy and uncomfortable period.This period was on time and seemed normal to what im used to. yesterday i had to take two pills in one day because i forgot a day and now im starting to feel period like symptoms with brownish bleeding, im having slight cramps and im very fatigue. the bleeding is also thick. i took a pregnancy test last week which came out negative. Should i be concerned?