Brown blood

So, I started my second period a week ago and the first day it was red (the blood) for like 2 hours but then it started getting brown and I thought “okay it’s just the blood from my old period and it will soon be red again” so I didn’t stress at all but then the second day it was still brown so I started worrying a little third day still brown fourth still brown and then fifth STILL BROWN at the point my period stopped (the blood was really dry and brown like I said) what could it be and what should I do