Bleeding while on Depo Shot

Hannah
I've been on the Depo shot for a year now and I usually don't have any bleeding. Me and my boyfriend don't use any protection other than my shot. Lately I've been having a lot of spotting and I can tell some is new blood and some is old blood. I just don't know if this is normal or if I should be worried I'm pregnant or miscarrying or something? 
Any advice will help, thank you😊