Hi Annie,
I had this too! Its gone now but drove me crazy. My Doctor couldn't work it out and Oncologist said probably caused by chemo. I even went to the Dentist and had all my silver fillings replaced with tooth coloured amalgam ones. I finally just forgot about it and accepted it. Mine was more in the saliva or back of my throat. Its gone now anyway and I'm 3.5 yrs post Chemo. Probably went last year. Can't remember. So hang in there!!
Just an aside - can you change Tamoxifen brands? I've tried a few generic ones over the years and some seem less offensive. Maybe that would help?
Also have you had a good check to see that you are still cancer free? Just a thought.....
All the best, Diane