What Causes Thick And Lumpy Vaginal Discharges?

Hi, I am on the contraception pill and may have missed it for one dy if at all and since I hav had brown, thick discharge with a little blood. It has bn happening for about a wk now, although the lst time i had sex a clumpy brown, stringy bit of discharge came out. My concerning problem is Today there was quite a large lump of sturdy but stringy like discharge in my pants, the only way i can describe this today was as if a bit of tissue/fat had come out of my vagina. Can anyone help?