A 15 year old guy and I need to gain weight, I am 5'7" and I weight 110?

Ok, All I want to gain is like 10, or 15 pounds maximum. Im hypoglycemic as well. The nutritionist gave us a diet for me based on my underweight and the condition I just told you about. But the problem is that the diet is rather costly and we only afford for me to eat like that for only 2 days a week or so. The diet consists of a 2500 calorie die, and the problem is that I hardly have an appetite. Would it be good for me to eat half pound of bread, and 4 spoonfuls of peanut er a day? I am also taking Centrum at the moment. I am also abit frail and weak, I would like to join a gym as soon as I gain those pounds. What can I do? I walk like 2 miles a day for obligation to walk to school.