Brown discharge

Hi guys , 

I'm really worried about my self I'm 18 years old never been on a website like this before never opened up to anyone  about my private problems ,but as I'm really worried I hope someone could help me . So straight after my period I had this clear water coming out of my vegina .after a few days it turned to brown and it looked like brown blood the smell was awful could literally say it smell like poo it's been 3 weeks not and there no improvement at all it not going ,it's just getting worse , could anyone help me please or anyone know what could be wrong with me ?