White coating inner mouth like cheeks and lips..dry mouth.?

This problem started about 6 to 10 months ago.at first i used to get dry mouth that is my mouth used to be constantly dry all the time.then about 4 months back i suddenly noticed that my inner lip was turning white and gradually after several days my whole inner mouth was white in colour.pls note that it is not patchy or a lesion.it is like a skin forming in the inner cheeks and lips only.my tongue is fine,and my pallette is fine too.its only my cheeks and lips and my mouth is dry constantly no matter what.i,ve been to various doctors and tried many medicines still no results.one doctor thought it might be due to the ulcers he suspects in my stomach..i dont know what it is,i'm scared its getting worse and i dont sleep with my mouth open.pls dont answer by telling me 2 change my toothpaste or that this is thrush cause its not.and yes i do smoke and tends to dry my mouth..infact when ever i get up i first smoke and have my coffee and smoke about 3 cigarettes before i brush my teets but if it was due to this it should have been gone now since iv stopped this long time back.pls help me what i should do since no doc is able to solve my problem..i think its some kind of bacteria infection cause it happens in the mouth when i get up and i get flegm that looks like this stuff in my mouth.