In your situation, I would find a Lyme
specialist, an LLMD (patient slang for a 'Lyme
-literate MD', meaning a doc who takes Lyme
and its coinfections more seriously than it seems your docs do). I went through 20 docs before getting a Lyme diagnosis, so been there, done that.
Rheumatologists are among the 'Lyme deniers' who do not take it seriously, so I'm not surprised at the reaction you got. I'd move on.
Interesting that magnesium helps you ...