Welcome to the forum, 2brits.
I had a bad case of paraflu a few weeks ago, sore throat, couldn't swallow saliva, got dehydrated. I went to the Emergency Room and got admitted for the dehydration. Along with the fluids in the IV I got a little dilaudid. You might try that. Make sure to tell them you can't swallow anything at all! They are likely to not give you all you wan't, but maybe you can get a little relief. Dehydration is serious.
The pain will end eventually.
If your doctor doesn't know what meds are no longer being made, maybe it's time to find a new doctor for the next problem.
When I was maybe 10, I had tonsils out. All I could eat was watermelon. They usually give you ice cream or popsicles, but those hurt too.