Hello. I have a problem with my tongue. It goes in cycles. Starting with a white coating, feeling dry and salty for a few days. Then this starts to ease. An oval mark then appears to the back of my tongue, usually dark red but occasionally purple. Then the next day it is surrounded by a raised yeloow-ish, pink circle. Then the mark fades back to the same colour as my tongue but still encircled. The raised circle then becomes flush with my tongue. Sometimes it stays the same size, sometimes it grows in size. Then my tongue becomes white again. When it turns pink again, it is unusually shiny. Then the tongue looks quite normal for a few days before it all starts again. The cycle lasts about 3 weeks. Do you have any idea what this could be please?