Hi I had what looked like implantation bleeding on the tenth day after my last period and I missed my next period on the 12th of this month but pregnancy tests were negative. I have had a lot of heartburn and some weird abdomonal cramping and last wed I started what I'm thinking is my period it started heavy for 5-6 days now is light and dark brownish and red and have had blood clots all throughout the last week, Still having abdominal cramping and last couple of days non-constant (it comes and goes throughout the day) pressure in abdomonal area worse when sitting and I slouch or hunch over. Is this anything to be concerned about everything was normal and regular until now. What is this?