I've Had The Depo Shot 3 Years In A Row

I've had the Depo shot 3 years in a row & always the day I was due I got my period back woke up & red blood . My last needle was due March 24th but I didn't get it & didn't have blood. Although was on medication . On March 14,15,16&18th I had pink & clear stuff when I wiped than nothing .
April 25th being over a month since not getting it I had brown spotting only lasted 3 wipes than nothing & nothing today .
I'm confused cos I've always bleed when I've been due for it & I haven't had blood :/