ok lots of details I know but they are important i think

I am on depo.... I was on it for a year with no problems went off for a few months and have been back on it for approximatly 6 months now. I do not have a period when I am on it. not even spotting.... I have had massive weight loss (healthy weight loss) in the past 8 months about 100 lbs... (doing it the right way eating right and exercising) I have not been extremly sexually active the past 6 months until the past month... last week approx 6 days ago I started spotting off and on... I would spot a couple of hours then gone for a couple then back.... yesterday it got slightly heavier but followed the same pattern.... today it was like a flood gate opened and I have huge black slimy things in it... it is also bright red.... I have never had this happen... should I be concerned or could it be becouse my hormones have changed with the weight loss and this is just build up that needed to be gotten rid of...

also not much pain.... more pressure then pain....