Why Do I Get A Bitter Taste In The Back

Why do I get a bitter taste in the back part of my mouth when I eat. After eating the bitter taste goes away. I often can smell an unusual odor. Could this be due to medication. Ive had an cat scan, blood tests, stool test. Nothing. Liver count was elevated but has returned to normal. I took, steroids and atibiodics for infection that is gone now, pain injection in my back for pinched nerve and loads of pain medicine. Nerve pain is gone now and haven't taken any of those mentioned medicines for some time now. Just got the bitter test and smell.