brown discharge for weeks

the last time i had sex was dec 15 and i’ve had brown discharge since the 22nd of dec and had a 3 day period with 1 1/2 days of light bleeding after abt a week after the discharge started. my period was heavy and bright red with bad cramps but it was way shorter than my usual. i’m now feeling a tightness or almost like my lower right abdomen is swelling but it’s not swelling along with brown discharge still. the discharge is dark brown. would anyone know what’s causing this???? and possibly how i could fix it??