Period, Birth Control, and Fasting...

2 months ago I got the depo provera shot. I'd had it two years before and my period stopped completely for the entire 3 months. However, I'm doing a prolonged fast for personal reasons, and the last two weeks have been having light bleeding (dark brown) which escalated to pretty much being on my period...all dark brown blood. I've had sex in the last 2 months, about 5 times and I'm hoping I'm not pregnant and that it's just the combination of birth control and my fasting. I'd really like some opinions, though. Why would the blood be so dark brown and no red at all? And why have I been bleeding for so long?

Thank you in advance...