Hi So I've Been In The Implanon For About A

hi so I've been in the implanon for about a year now and I have not experienced any bleeding for the full year but for 2 weeks now I've been getting this dark brown discharge some days its very light and some days its a bit heavier or stops cinpletely its not like a regular period though. I would just like to know what the cause is and also if this is normal and how long it will last , do I need to be concerned, ?