Yes I Have Been Off Depo Since September... The First

Yes i have been off depo since September... The first month in October I didn't have a period but in November I returned to a normal period December I bled a brown discharge and blood mingled this month brown discharge. All of my cycles have been abnormal. Took a total of 3 pregnancy test the last being yesterday and had sex last dev 31.... However as I stated the brown discharge was happening before then.... What the heck is going on?????