For what it's worth, I've had some success treating my Long Covid symptoms with a specific form of Tryptophan found in Hydrolyzed Whey Protein (a standard bodybuilding protein powder.) You can get it OTC from Amazon [1]. My symptoms are slightly different from yours but sound close enough.

A recent study showed that persistent viral infection can block normal tryptophan receptors [2] which causes a diminished ability to synthesize serotonin, which it turns out is pretty essential for a lot of things including alertness & sleep, etc etc.

The tryptophan found in hydrolyzed whey binds to a different receptor than normal dietary tryptophan, thereby allowing your body to reuptake it and produce serotonin as usual. (This is all in the study.)

A word of warning: If you do this, take only a very small amount to start, maybe a quarter serving, because even though the body rate-limits serotonin production your tolerance will likely be extremely low from not having much for years. I didn't know this and I took a couple servings per day (after all, it's just protein powder right?) but by day two I was hypomanic which was unpleasant and it took about a week to return to normal. So start with maybe a quarter serving, wait a few days, and repeat until your serotonin normalizes.

Also DON'T TAKE THIS if you're on any medication that interacts with serotonin such as an antidepressant, SSRI, MAOI, or what-have-you. I am not a doctor and this is not medical advice, just something that helped me after many years of difficulty.