Implantation bleeding or...

Nicole
So since yesterday I have experienced a light brown tinted discharge; but it doesn't show on my underwear only when I wipe or actually stick my finger in to check. I have no cramps or signs of my period and haven't had my period since I took my DEPO shot in June. Haven't taken another shot and I was just wondering if this could be implantation bleeding or just the start of my period coming back