light period for 10 days???

Well I recently got the depo shot a few weeks ago and my period was about 5 days late and then when I got it it's just been brown spotting for the past 10 days. My period is usually pretty normal and lasts about 6 or 7 days. This is really weird for me. I haven't taken a pregnancy test at all but is it possible that I could of gotten pregnant around the time I got the depo shot. Or does it sound like this is just because of the depo shot? I'm not sure.... I really hope I'm not pregnant considering I just turned 20 and already have a 1 year old. Help?