Brown Discharge After Period??

So my period ended 2 days ago. Since ending, yesterday I had a little bit of dark brown discharge on my underwear. I changed them, wiped up and carried on. Today, I have a lot more discharge and it's so weird. I've never had discharge like this before and it's so dark and there's a lot more of it. What could be the cause of this??? I googled and saw endometriosis which is freaking me out as we have been trying unsuccessfully for 10 months.