Im doing p90x and i'd like to put on more weight.....help?

I've been doing P90x for a while now, I just started a new job where im out walking all day reading hydro and water meters and im starting too loose weight unfortunately. In the beginning I was eating alot because I was at home and the fridge was right there. I noticed the weight gaining and it wasn't fat and I was feeling good not bloated or anything. But now I'm usually just having a bowl of cereal before work because it so early (I'm not a morning person) then a granola bar or two between then and lunch. For lunch its a bun loaded with toppings, a yogurt, and a cheese string. Then not much till supper where I usually have a good big meal. Then after the workout I have a protein shake, and an hour or soo after that a I have a small snack, cheese and crackers, fruit, etc etc really depends on the time and how hungry I am.