What Causes Brown Vaginal Bleeding After A C-section?

I had a c-section 6 weeks and 2 days ago, I stopped bleeding 3 weeks ago and last night had some light red bleeding. I thought it was my first period already, have been moody this week and breasts were sore. Now 24 hours later my discharge is no longer red but a very very dark brown it is very thick and sticky in consistency but there is no odor at all, no cramping or fever I feel totally fine. Not sure if it s info that os needed but did resume sex after not bleeding for 3 days 3 weeks ago. I had my fallopian tubes removed so I know pregnancy is no possibility.