So I took the Amoxicillin+Metronidazol some time ago. The Metronidazol I think messes your brain up quite a lot. I would recommend not expecting to be able to work much. I was even too scared to drive a car. (google for the words Metronidazol confusion, it apparantly even has the power to destroy dopamine+serotonine..)
But I pushed through it and survived the 7 days.
I took plenty of probiotics (both food probiotics and probiotic drops from the pharmacy) once per day, some hours away from the previous and next antibiotic dose.
I also took NAC and Vitamin B to counter the Metronidazol effects.
So I think my digestion is fine, It didn't havoc my gut.
My gums don't bleed anymore when flossing and also don't seem to feel inflamed and hurt anymore. I also didn't get headache anymore since then.
For POIS it did not change that much, maybe I don't get sore throat anymore?
It's definitely a piece in the puzzle (making POIS worse) but not the root cause for sure.
The biggest positive health effect I have right now is still the
increased salt+electrolytes+fluid(German alcohol free wheat beet) intake I'm doing.