I found a thin yellow coat on my tongue. What can cause this problem. Also my nose drains bad at night. Can this b the cause of this problem?

Could be. A post nasal drip, allergies or a sinus infections can lead to a coated tongue. Clean your tongue by brushing it or using a tongue scraper will remove the coating and help keep your breath feesher. Treating the sinus problem or allergies will provide long term solution.