You should experiment with calorie-dense foods to see what works for you. I do very well with oatmeal, rice, chicken, and fish. I have significantly slowed -- but have not entirely eliminated -- my weight loss by eating just enough of those foods to trigger symptoms and stopping there. Like you, I'm still trying to figure out how to gain weight, but I've been able to slow my weight loss quite a bit (from one pound a week to one pound every two or three weeks) with the above diet. I have to start with a bowl of oatmeal first thing when I roll out of bed at 6 and keep eating every two or three hours until 7 at night. Obviously those specific foods may not work for you, but you need to experiment with high calorie foods until you find something that works.