Any ideas? Did anyone else notice a connection between stool and how they feel?

I have had Long COVID since 2020. Since my first COVID infection, my stool has never been normal. It is usually yellow, soft, and not the normal dark brown color I had before COVID. Recently, I started taking Valtrex, ketotifen, and nattoserra (nattokinase + serrapeptase).

I slowly started feeling better, and then something very strange happened. For about 15 days, I felt almost like my old healthy self. This was the first and only time since 2020 that I felt this good. At the exact same time, my stool completely changed. It became dark brown, normal-looking, and much healthier. This was very different from my normal yellow/soft stool. I did not make any other big changes during this time.

Then, while I was feeling very good, I went outside with a friend and did much more activity than usual. The next day, I suddenly felt like my old Long COVID self again. My other symptoms came back, and after that, my stool also went back to being yellow and soft. Im still same. I know this does not prove that the treatment caused it, because I started three things at the same time. But I really want to understand the stool part.

What could cause stool to change from yellow/soft to normal dark brown when my overall health improves? Could this be related to bile, digestion, gut movement, pancreatic function, gut bacteria, inflammation, or something else? Has anyone with Long COVID or ME/CFS experienced something similar, where their stool became normal during a period when their other symptoms also improved?