Period problems

So my cycle is normally 35 days, 6 day period. But since I started the Depo shot Jan 11. 2016. My cycles has been so off. Went two months with no period, then got it for 3 days. Now it went 25 days and my period is on day number 8?! I've never ever had a period last long than 6 days.... It's not heavy what so ever and the majority of it is old brown blood... When will it end?! It's just getting annoying now.. No cramps no nothing. Just very very light spotting. Help