Help pls

Sorry may be a bit TMI

Last week I had brown spotting for like 3 days and bad diarrhea and just stopped all of a sudden then today I had the bad diarrhea and I am currently 18 days late. Took a test last Tuesday and it was negative. I'm overweight and have hypothyroidism but am on regular medication for it.

Sick and tired of going to the doctors and being told nothing is wrong. I'm not 100% sure if I have ovulated as my fertility doc told me 3 weeks ago that I haven't ovulated So what could it possibly be? Could I be pregnant or is it period coming?