I have this too. I can be hungry during the day, but once dinner time comes, my appetite is gone!

I also go in cycles... not hungry much (like now) and then 2 weeks later, very hungry!

When I am upset, I tend to not eat. (which is the reverse of most people). Perhaps your impending surgery?

Things to focus on before and after, are adequate quality protein (if you are in the mood Whey protein is very good for tissue repair), and a quality zinc supplement. Vitamin C as well.
If you have a good senior multivitamin, that should do. Just have extra oranges, etc or take another Vit C. Vit C can help keep inflammatory cytokines in check so there may be less fibrosis/scarring, internally.