Hi. Sorry to hear you're in this situation.

All sorts of side effects are possible - Merck's website documents Keytruda's - you'll probably experience some but not all of them to a greater or lesser degree. There is no "normal". Full disclosure to the doctor/consultant is a must.

I'm on Keytruda. What I found helpful that you might find relevant was:

Fatigue: Creatine Monohydrate (CM). It's produced naturally in the muscles, but is also used by the brain. If the body is less physically active then less CM is made, so there's less available for the brain. Result: tiredness. A small top-up by supplementing can help. As always, discuss any advice you get (like this) with your doctor first.

Appetite: cheat! I make "food" drinks, which are easier to down than meals. I crack a couple of eggs and make up to half pint of milk, whipped up. Warm up in the microwave (not too much or it starts to cook!) Complan works too (cheapest is from Amazon.) Soups as well ("chunky" soups even better, so blend them down to liquid.)

kind regards
Steve