string/brown discharge

i have been on birth control (depo shot) for about about 5 months and i’ve had no problems with it because i have been on it before. i normally don’t have any periods while on the shot. but recently when i go to the bathroom i’ll notice that there is a brown/dark stringy looking like discharge or clots??? some days there won’t be any discharge some days there will. i’m not sure why or what is is??? can anyone help or does anyone know?