Hi hehe1,
My brother had the same problem as you, always wanting to increase his weight and unable to do so, but he overcame it by using a combination of diet and weight training.
He lifted weights three times a week doing squats, bench presses, clean and press, chins etc. All the exercises primarily used for the fastest muscle and strength gains.
As for his diet, he ate small meals regularly throughout the day so that his body was never over-loaded with food and so there was a lot less problems with digestion. His diet consisted of fruit and veg, meat, fish, scrambled eggs, wholemeal bread, oatmeal; all good quality food in fairly small portions, but spread out so that he was getting plenty of food throughout the day without ever having the feeling he was forcing himself to eat. In this way the fact that his appetite was poor became less of a problem and he was able to get all the nutrition he needed.
The other thing he did though, and this might be the key for speeding up your weight gaining was to drink plenty of milk. I don't know if you are able to do this if you have some problems with digestion, but if your appetite is poor it's obviously a lot easier to drink more calories than it is to eat them. He used to have a glass each time he ate, and was convinced it helped him with his muscle growth too.
Something else I believe is that regular exercise really helps with appitite and digestion as well as all round health, so if your not taking regular exercise, perhaps that might help you out?
Good luck.
