Ugh what is coming out of me!! Please please give your opinion!

So it’s been about 15 weeks now since I’ve not had a period and now I’m having super dark brown (looks like mud almost) stuff come out of me and I seriously have no idea what happening and it started yesterday but it’s so light to where if I just have a liner on it’s ok. But I’ve had 2 different times where I have very bright red spotting for a hr or so but that was it

I’m supposed to go get blood work and an ultrasound done on Wednesday and then a follow up appointment on Monday to see what my results are. I would post a picture but it’s super gross so I’ll spare ya that