firstly congrats on your pregnancy
i have been through the same thing, i had a very large perigestional haemorrhage from 12-23 weeks with my 5th babe
when i was 12 weeks i was coming home from shopping and i felt a huge gush while driving, got home ran to the toilet sat down and felt more gushing wiped and saw A LOT of bright red blood, i was sure i was loosing the baby, went to the ED got seen right away, they did a quick scan with a crappy machine as it was about 9pm by this point, and they told me 'off the books' baby was alive and i needed to come back in the morning for a proper scan.
the next day i had the follow up scan and was asked right away if i had had any trauma because the bleed was so big and they dont usually see that kind of thing with out something bad that had of happened it was from one side of the placenta to the other all over the front of the gestational sac the good thing was the bleeding wasnt coming from behind the placenta.

you can see them measuring the bleed here, this was at 13 week i think
i had several scans over the few weeks after this, and it always stayed very large, and as my boy got bigger and started kicking i would bleed, every few days i was loosing a lot of bright red blood, at 17w i woke up to a gush, went to the toilet where there was a huge amount of brown, like what you described, i called my IM (L was a supposed to be a homebirth) she said it was a good sign, meaning the clot had come away and was old blood, but over the course of the day, it turned red again, it was like the old blood would come away and a new bleed would start.
at 22w6d i had my last episode of bleeding.
my son was born at 30w but they said it had nothing to do with the bleed, he was a c/s and they saw no evidence of the haemorrhage, to it healed somewhere between 23 and 30 weeks
L is now 1yo and happy an healthy
sending you love and hope all goes well, and i know how scary it is to see blood when you are pregnant, hope the rest of your pregnancy goes smoothly xo