This is not intended to be medical advice for your situation. I am a dentist and also a person who has had numerous medical issues including radiation induced neuropathy. . Taste and smell are all part of the olfactory nerve system. Although they are not sure how Covid affects this system, it would seem to be that the sooner one tries to mitigate the symptoms the better. Like a neuropathy. If it were me I would have asked to be placed on a low dose of Neurontin and Motrin. Neruontin seems to help surface/diabetice vs deep) neuropathy and pain. Retraining smell is smoke and mirrors to me. The sensory nerves got damaged due to the virus. The nerves need to be calmed down and hopefully regenerate or form secondary nerves. Don't give up hope. For the pain in the back of the tongue, it may be a good sign that something is still active. Most mouth washes have a lot of additives like citric acid or preservatives. Simple food grade glycerin rinse, coconut oil or slipper elm lozenges may help. Water down simple no dye Listerine to keep it clean. On the side, I have given patients an oral rinse of Dexamethasone no dyes( the doctor needs to look it up but it does exist) It does wonders for autoimmune oral burning due to Lichen Planus. You rinse, hold it in the back and you can swallow a small amount . Come to think of it , I might add a small dose of low dose of oral prednisone for a month or two. LOW dose ( not a med pack), 5 mg not more/day. This is what I would be asking for if it were me.
I hope this helps.