Symptoms are. a yellowish substance on tounge wich i scrape off and comes back in a few hours.same smelling gas. all the time no matter what i eat.

See Dentist: I suspect candidiasis infection (thrush) though without seeing it it is hard to tell. You need to have it looked at. Also, i don't know if you smoke - that can cause discoloration & diet can affect the odors as can improper hygiene. Your dentist can evaluate & prescribe appropriate treatment.

Infection: sounds like anaerobic bacteria. check with oral surgeon.