I Have Been On Birth Control For 7 Years. I

I have been on birth control for 7 years. I take it regularly. About 2 weeks ago my boyfriend and I had unprotected sex but he did not go inside of me. I have not missed any pills. It is now a week before my period and I have been having light spotting for 3 days, sometimes bright red and sometimes brown. Recently, my boyfriend and I broke up, I have been working out, and I've switched to a healthier diet. What could be the cause for this spotting? Stress? Diet/exercise change?