Discharge ???

I’m an 18 year old female , on birth control ( Nexplanon ) , and I am sexually active . Since I’ve been on birth control I have only gotten my period once and it lasted two weeks . Since then , nothing . Up until about a week and a half ago , I’ve been getting nasty brown discharge . It makes my pee smell SO bad , I’ve also been cramping a little . And it’s been going on for going on almost two weeks . And when I wipe , it’s also on the toilet paper .... what is going on ??