I noticed stains in between my teeth in the past month that came on suddenly. I brush twice a day and floss daily. Only between my teeth are stained, the rest of my tooth is pretty white. I don't drink coffee/tea or smoke. What could be some possible caus

Stains. There could be a number of different causes. Coffee/tea/tobacco are not the only things that can stain teeth. If you have not seen a dentist or had your teeth cleaned by a dental hygienist lately then that would be a good place to start. Chances are it's just tartar that needs to be removed, but it could also be the start of a cavity, or a leaky silver filling.