What Causes Dark Brown Vaginal Discharge?

hi, i was on depo provera for almost 1 year i never had a period or spotting, when i got off of it ,there still was no sighn of my period. I havent got my period in a year,but 2days ago i started to get like a dark brown discharge im not sure what it might be? im also very scared i wont be able to get pregnant i do want to have kids soon so i was also wondering how can i get everything back to normal? -Thank you