13 weeks postpartum brown discharge

I had something similar around that time after my C-sect and honestly it did freak me out a bit, but my PD told me that light discharge can linger or come back especially when you are breastfeeding because your hormones are all over the place. That said, "thick" is the part that would make me want to get it checked rather than just wait and see, because thick discharge can sometimes mean something needs attention. I would bring it up with your gynae or at least a polyclinic visit soon, just to be safe and get peace of mind. Do not let it sit too long if it gets heavier or has an unusual smell.

Brown discharge at 13 weeks postpartum can sometimes be the start of your period returning, especially since breastfeeding can cause it to come back in irregular ways at first. That said, since you had a csect, it is really worth bringing this up with your gynae or at least your polyclinic doctor just to be safe and get a proper check. It is totally understandable to feel worried but you are doing the right thing by flagging it early, so please do not sit on it too long.