How can I gain weight like this?

I hate being thin, I want to get fatter but I am finding it hard since I am allergic to most fattening food products like meet and cheese and chocolate and egg yoke which is in most cakes and sweet stuff so I need a positive way to gain, what foods should I eat? should I eat more of the stuff i do eat? no pills or anything though. I have tried one gain weight shake but I am not sure if it is puting weight on or taking it off