Spotting?

Heather
Hi. So due to irregular periods for years it never bothered me then.  A year or so ago my ob put me on pills to help regulate me. I stopped taking them a while ago and 9/10 I do have a monthly period. I also work with a lot of females. Normally it lasts a few days. This month about 10 days ago I had a "normal" 3 day cycle. I started spotting reddish brown today. Any thoughts why this might be?