Possibly pregnant.. or not?

I'm on birth control, and about 2-3 weeks ago was the last time I had sex. I stopped my birth control for my period, and it was super light and I was getting a lot of dark brown discharge. The way my uterus is shaped my doctor previously told me its a high chance I can miscarry if pregnant.And I've been having no symptoms of pregnancy. Would the really dark discharge be a symptom of pregnancy? miscarriage if pregnant? or just a light period? I'm planning on taking a test monday but its just been stressing me out.