Spotting after running? Should I be worried?

Just got a first faint positive 2 days ago at 8 dpo (so I’m only 3 weeks 2 days today) and sticks have been progressing nicely. I went for a 3 mile run, which is very normal for me, and I had a small amount of brown spotting in my underwear afterwards. There was no more when I wiped and no more since.

Was this just cervical irritation or is it the start of a chemical? Has this happened to anyone else and everything be fine? Is it even worth calling my OB since I’m so early? I’m so worried…