I need to gain weight!?

I have Crohn's disease and my weight is steadily falling. I went from 115 to 110. I know that doesn't sound like alot of weight loss, but I'm a stick. I'm 5'7 and I want to look healthy. I don't have a healthy appetite because of the Crohns. Is there anyone else who has dealt with this? Is there any thing on the market for this?