What Causes Brown Vaginal Discharge After Stopping Birth Control Pills?

So I was on Ava birth control for 5 months without having my period once, and on the 5th pack I wanted to have my period and stop the pill after that, so on the 3rd yellow pill I got my period and I had it for about 3 days but then it just turned into brown/ black discharge and only a small amount of it and now I've have that for 11 days, and I just want to know when it will end as what is it??