Have you tried to supplement your diet with protein drinks (and I dont mean Guinness!!!)
I needed to put on some weight many years ago and used Complan. Basically I drank 3 Complan drinks (with milk) a day, after meals. If I recall rightly this was about an extra 7000 calories a week which equated to about 2lbs of weight per week. The reason I used a drink is because I found it impossible to eat more but to drink more as not a problem.
Any weight gain/loss program should be looked at properly to ensure that all exercises and foods are appropriate and managed. speak to your doctor and/or an instructor at your local gym.