What Causes Spotting Without Actual Menstrual Bleed?

Hi Doc, I'm 39 yrs old. I've always had regular cycles, my periods always lasting 5 days. My last period, however, lasted 7 days, then I had one brown spotting on Day 9. Everything was normal after that. But yesterday, Day 26, I had one pink spotting, but no menstruation yet till now. I had cramping earlier though. Is this something to worry about? It's not the first time I had spotting a day or two before my period. Btw, I am not sexually active. Thank you very much.