Ewww... why does it look like that....?

so lately my tongue has been turning yellow. i can brush it right off but it comes right back in a couple hours. i cant taste it or anything. its just yellow. my mom thinks its because i eat too much acidic food (i eat tons of tomatoes and drink a lot of orange juice.) any other ideas what it could be? im going to the doctors soon for a check up but until then id like to know whats going on.