What Causes Brownish Discharge After Giving Birth?

Hi, Ive been having a brown ish thick discharge now for about 2 weeks, i feel fine in my self. I gave birth 17 weeks ago and had a NVD, no stitches etc. I have seen had the contraceptive injection since which i havent had before, but that was in june. Before i came pregnant i had thr implant. Please help as there is family history of cervical cancer. Im 24 years old