Hi Sandra, I can relate to your eating problem as I'm often much the same. Pain and meds plus lack of sleep all add up and food has no real interest usually.
I'll have a bit of fruit for lunch and a few nuts.

We dream of a food pill-how much easier would that make life?

All the hassle and bother of preparing and eating food.

Glad to see you single out protein, as it's so easy with manufactured 'foods' to be way to high on carbs and too low on protein. There is a balance that should be achieved.

Smoothies are a definite option-you may have to experiment with taste and texture.
One thing that we have regularly is a smoothie made with coconut cream, fresh fruit (berries are the best), water and ice cubes.

You could add protein powder or eggs.

Are you able to eat nuts? A bowl of mixed nuts. preferably raw, is a handy snack. We do almonds, hazels, cashews and brazils.

What about juiced vegetables and fruit? Good for nutritional balance, and you can add things to take away sweetness.

It's probably a good thing that sweetness is not wanted, as it's so easy otherwise to fall into the cake and biscuits trap.

Sorry that I can't offer anything more than this. I can certainly understand where you are coming from though.

Things that you can eat will need to be rotated as you very soon become either bored or averse to a limited menu. So look for several options if you can.
Maintaining nutrition will be a challenge, so what about supplements as well?