Inexpensive meals and snacks to help gain weight while being lactose intolerant.

Didnt know where to post. Figured this would be a food start

Last time I checked (not often), Im 5’6 and 100lbs. Im male. Apparently thats not good. For rhe longest I would eat chicken whenever I could, drink 1 Muscle milk a day, and occasionally splurge on spaghetti from a pizzeria. Now I eat chicken pot pies ($10 for 4 from Walmart) and sweet and sour chicken (2 a day/ $2 for 1 and Walmart). They are good, but cause me to go to the bathroom all the time. And now that I may be lactose intolerant (self discovery; not verified by a doctor), that reduces what I can eat. I know that can be important towards an healthy diet and gaining weight. All this at the same time while trying to save as much money as possible.

I want to know what is a good and quick breakfast, snack, and filling dinner to have every day at work to help gain weight.