How to get rid of stains inbetween my teeth?

so i have horrible brown stains inbetween almost all of my teeth. i use whitening toothpaste which works amazing on my teeth, but seems to miss inbetween them. its annoying me, because i try really hard to get my toothbrush and the toothpaste inbetween my teeth, and ive been using this everyday for over a month. i also floss, and use mouthwash. what else can i do? it looks as though i take no care at all, and having such a low self esteme, this is killing me. all advice is appretiated! thanks x