I feel ya, I'm 24 and under weight.. I eat all the time, if I slow down just a little bit my weight nose dives.. Eatting 120-140 grams of carbs for lunch is not uncommon for me, even then a hr or two later I'm starving again.. I try not to snack if I can help it, I just dont like taking the time to correct for it mostly, so I eat quite a bit during meals so that I'm not so hungry during the rest of the day.. If I do snack ( normally peanut butter samwiches, good stuff

2 of them helps me fill full for quite a while ), I know how much insulin I need for what I eat. Just check my BG before and about 1 1/2 hrs later..
My insulin to carb ratio is 1 unit to 20 grams, it's been really close to that for the almost 5 yrs I've been diabetic.. Once ya figure out what yours is, then it makes it SO MUCH easier, it is worth the trial and error figuring it out.. If you find yourself staying a tad high when not eatting, you could even increase your long lasting insulin, this is what I had to do to stay half way stable during the day..