Spotting after two months on depo?

Basically i got my depo after giving birth at my 6 week appointment, i never even got my first period back. Two months ive been on depo (no period) and suddenly spotting for three days now. At first i thought it was because me and my husband had sex and ive been easily irritated and redness since giving birth so during sex i thought i just cut myself a small bit, its happened before from friction. But im actually like spotting cuz the spotting has messed up underwear, its light and i don't look like im discharging blood at all, its all i can think of because i see no cuts and i have no pain. When i wipe its light pink Could it be the depo? Why would i get spotting now after all this time?