What do you think this could be?

I got the depo shot in March after having my baby in February. I've been having unprotected sex since then always pulling out, I was suposed to get another shot in the beginning of June but I didn't like the effects of depo so I didn't get it. We still have sex without a condom, but he pulls out every time. earlier I noticed there was some dark blood in my undies, so I figured I was starting my Period. My first one since before I was pregnant. But I haven't bled very much, and usually after I start it starts to get heavier very soon after it starts, but it's been light since it started hours ago. I went pee before I went to bed and there was only a little bright red blood when I wiped. I'm having some cramping as well. Do you think this is my period and it's just taking a bit to kick in? Thanks in advance for answers!