Spotting between periods.?

So I've been on the pill for about three years now. I started spotting last Saturday (Aug. 23rd). I'm still spotting today. I am sexually active but haven't had intercourse for over a month. I know my cycle and I started my period on time last month and I don't have any signs of pregnancy. I'm supposed to be starting my period tomorrow. I'm not thinking it's any kind of infection either. I don't have any other symptoms other than the spotting.

I have never spotted between periods before, so I guess my question is if it's normal to have this kind of spotting while on the pill.