Hi I Have Been Getting Brown Discharge On And Off

Hi I have been getting brown discharge on and off for the past month. I have been std checked and it came back negative which is good. I got the implanon insert in my arm around the end of June 2016 and hasn't had any period or discharge until I was fingered at the beginning of December. I had brown discharge for 2 weeks, then it stopped and now it's back again. Do you just think it's old blood shedding?