Bleeding on depo?? Why???

Nyla • Living 20 and carefree in the big LV

So I’ve been on the depo shot for like 4 years now and I haven’t had a period in over a year yet for some reason I am bleeding in between my last and next shot. It’s not brown like old blood but red like fresh new blood and I have cramps and all any advice wth do I do to make it stop?