Depo shot

Hi everyone! I'm Ciera and I have a concern. I've been on the shot for 3 years and almost 11 months and I don't have a period with it. Well Saturday I went on a community walk and when I got home I was cramping so bad. So when I went to the bathroom to use toilet my undies was clear but when I wiped I had this mucous brown discharge. So early this morning around 5 am I went to the bathroom and it was red/pinkish in color. Now it's back to the brown. My shot isn't due till in between Oct. 20-Nov. 3. What do you guys think this could be? Unexpected period maybe?