Bleeding

Okay ladies. I'm almost 6 months postpartum. I got the depo shot a month after delivery. I was due for another one March 9th, but didn't get it due to insurance reasons. Before I begin, keep in mind that before my pregnancy, my regular periods lasted no more than 3 day, and were regular flow. Okay well at the beginning of April I started bleeding. Well, spotting I suppose, for about a week and a half. Nothing that required a tampoon/pad. I just bleed a bit when I went to the bathroom. After a week and a half, I stopped spotting for a about 5 days and started spotting again. Then stopped again for about a week. We're now into May and I've just started spotting again today (May 3rd). Is this just from the depo shot I was on? Or what else could I be spotting so much for?? I had the depo a few years ago, and don't remember spotting like this when it ended then..