Late period

Okay so my periods are NOT regular, but typically my cycles are in between 26-29 days in between. This is cycle day 30 and still nothing. 2 days ago, I had brown spotting that day and the day before then it just stopped. I've taken like 4 pregnancy tests and they are all negative. We are NOT trying to conceive. Why could my period be so late? And what was up with the brown spotting??! 😁