Could Vaginal Spotting Be A Sign Of Pregnancy?

Hello. I'm sorry this isgoing to be long, and probably not an easy question to answer, but I am worried and need help! Okay, so on 2/26/10 I got my first depo provera shot, and the dr. told me to wait 2 weeks before having unprotected sex because the shot wont kick in yet. But I had unprotected sex on 3/10/10 and on 3/11/10 which is only 12-13 days so it wasnt quite 2 weeks. Could I be pregnant? Its now about 6 weeks or so later. I am supposed to get my period 4/17/10, but it came a week early and is really, really light. It's light enough that I don't even really have to wear a pad or anything. And I dont know if I'm just spotting, if it's implantation bleeding, or if it's light because of the shot. So I don't know what's going on, or if I'm pregnant, and if so will it harm the baby? Please Help!