If you think you have long Covid, you should do some research about CIRS (Chronic Inflammation Response Syndrome). It is a condition caused by exposure to toxic mold from water damaged (inside or out) buildings. There is growing evidence that there isn't actually a separate condition for long Covid, but rather it is Covid-triggered CIRS. (Lyme can trigger it too). (Note: only about 25% of people are genetically susceptible to suffering from CIRS)

CIRS causes your body's call-and-response immune system to short circuit; meaning one part detects the problem and the part is supposed to fix it but the part that is supposed to fix it (remove the mycotoxins) doesn't see the problem and does nothing. CIRS causes a lot of side effects, including all the ones mentioned by the GP and many more. If you want to test for toxic mold, you need to test the dust in your space. Some amount of mold is naturally in the air at all times. The dust will show and accumulation of mold over time and show if there is a real problem.

Source: I thought I had long Covid for a long time, until I realized the real problem which was toxic white mold in my house. I threw everything in a dumpster and sold my house and am now on the long slow multi-year process of recovery. If you think you may have it, try pushing Mg, Zinc and Potassium really hard for a few weeks. Take things that naturally bind the bile in your gut (the mycotoxins attach to the bile which is recycled). There are heavier binders that bind everything but I wouldn't start there.