TMI PHOTOS - Abnormal mid cycle bleeding

Okay, for the past 3-4 days I have been experiencing strange spotting & bleeding mid cycle. I tgought it might be ovulation spotting, but it has become too heavy & abnormal. This has never happened to me before. 
Friday it started with light pink & brown discharge, yesterday, it had escalated to red & brown bleeding & clots/discharge & there was some strange BLACK colored discharge/blood. I'm having some light cramping also. Any idea what could be happening? I have a dr appt this afternoon. 
My last period was 5 days late, also, if that makes a difference. I have endometriosis, my my periods are painful & heavy a lot of the time. But I have never experienced mid cycle bleeding. 
It's too heavy for just spotting, but a little too light for period. (Today it is back to just barely there light brown discharge)
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