Brown spotting but no AF

I keep getting brown spotting every month for about two days and then it goes away and I never get my period. It is actually lighter than spotting, i wouldn't even call it that. Idk when AF is due because I haven't had a period in years due to the depo shot. I have been off depo for two years and all I get is a tiny bit of brown here and there.. doctors have prescribed Provera and it hasn't helped. Idk what to do