I've been having dark brown sticky discharge for weeks ! i'm on depo-provera so i don't get my period . what could be? is it serious ?

Brown discharge: Usually, brown vaginal discharge is from old blood. You may have had some spotting - which can happen with certain forms of birth control like depo. There are other causes of spotting and abnormal vaginal bleeding/discharge including fibroids, pcos, ovulation, other medications and infections. Please contact your doctor to be evaluated! good luck!