Oral thrush or post nasal drip

Hello, I clean my tongue multiple times each day and use mouthwash daily. I get all of the white bacteria off my tongue except a patch at the very back of my tongue. Is this oral thrush? Also, can post nasal drip cause bacteria to form on my tongue?

http://imgur.com/qBjaXX1 Not my tongue but close enough

Also, after I clean my mouth and then close it, the white stuff is back towards the front of the tongue. Also, I'm coughing a lot and my throat is often sore. The ENT said I dont have tonsil stones. I drink a lot of water. I eat low amount of carbs and sugar