Can I gain weight from sitting down/ laying down all day?

I have been exercising lately for 2 times a day for 1 hour, but between them I just sit down or lay down on my bed watching tv or use a computer.... So can I gain weight from doing that? If yes, what can I do between my exercise not to gain weight, or calories.... Oh and I have been taking protein shakes 2 times a day after each exercise, and maybe a half cheese sandwich with whole grain bread soooo I don't take in a lot of calories. :)