Hello, I Have A Bitter Taste In My Mouth, It

Hello, I have a bitter taste in my mouth, it started about 6 months ago, just at night, it is now worse and is there all the time now. I have a hiatus hernia and have been taking daily medication for about two years. I also had FESS procedure about 4 months ago, but this problem started before that. My Dr has given me Gavisgon for 1 month but has made no difference.

Hope to get some help, thanks.