Spotting

I started Depo on September 24th and my period was supposed to come on Oct 10th. I know Depo can make your periods go from one extreme to the other, and yesterday I started having extremely light bleeding. It has continued through today. I have never spotted before so I'm not exactly sure what it's supposed to look like. How can I tell if I'm having a very light period or just spotting? If it helps, my boyfriend and I waited for the recommended period of time after the shot before we started having unprotected sex.