Could I be pregnant?

I've been with my boyfriend for 9 months I decided to go on the depo. Worst mistake ever! After I stopped using it which I only got it once. My period has been all over the place. My boyfriend and I haven't been careful. Recently this past week we've had sex 3 times none which we were careful. We're not opposed to having a child btw. I had my period last week and the last time we had sex was Tuesday. And today I started spotting but it looked like old blood really dark and all. Is there a chance that I could be pregnant? Please help!