After my ileo surgery 5 years ago, I was underweight too, and it took about 3 months before I started to gain some weight (now I have the opposite problem, am a little too healthy!). Ice cream (the full-fat variety) may help in your protein shake (I used to have a milkshake with every meal). I ate a lot of pasta with creamy sauces (alfredo, carbonara, mac+cheese, etc.), loaded mashed potatoes, any kind of potatoes for that matter, chips, fries, etc. Basically, go for all the stuff that dieters steer clear of: full-fat, full-cream, deep-fried, high carbohydrate; within reason, of course, make sure there is plenty of healthy stuff in there too. A balanced diet is the best in the long run, but high-carb food is good after surgery as it thickens output plus helps you increase your weight (and it tastes good too!). In my case, I was delighted to have a healthy appetite again. Give yourself some time, and hopefully, you will see the pounds gradually increase.