What Causes Dark Brown Discharge With Bleeding?

I have had dark brown discharge for over a week now with some (minimal) bleeding mixed in. The past two days I have found somewhat large pieces of skin being elimated as well when I remove my tampon. I was on the pill for 3 years and stopped for 3 months and am on my second month of a new pill now. I went through the first month on the new pill without any issues and had my period as normal when i was without the pill for three months. Any ideas??