Help!! Depo shot

I got the depo shot a few weeks ago and it seemed like my period was ending really early and the coloring of the blood is not right. So I posted something and someone said yeah that's normal. Well it's been about 4 weeks now and I'm still just lightly bleeding everyday.. Like spotting? The thing I am most worried about it the excruciating cramping. I woke up last night because of some pain and it's just in one or two spots and then goes away... Please tell me this is normal or what is going on??