Hold on, you may THINK you eat a lot of food but I 100% guarantee you eat like a pidgeon. I guarantee it. Simply eat healthy and eat like a ******* horse, I know the 'can't gain weight' dilemma as I was there not too long ago. But I now workout using Stronglifts 5x5 and get about 3300-4500 calories in per day, sometimes I push that higher if I feel like it. Whilst I still believe that eating way more than you need (even healthily) will make you fat, if you workout intensively like stronglifts - squatting 3x a week etc, you will not get fat. I don't agree with stronglifts recommendation of 5000 calories per day, but it's easily done. For instance, olive oil is 100 calories for 1 tablespoon/15 ml and you can just drop that over your meal (pasta, spaghetti, rice, all types of meat etc) if you need help getting up your calories. But I don't personally think you need to do that, simply eat calorie dense foods, for instance wholemeal pasta, Nuts, peanut butter etc. Drink more milk, I personally think the GOMAD (GAllon Of Milk A Day) approach is hard for those who can't regularly buy and store at least 1-2 gallon of milk per day. I get 1.2 litres in per day, almost 1/3 of a gallon and that's easily done.
Definitely start working out though, whilst stronglifts is a strength routine, for skinny beginners it will definitely add size to your frame, and after 6 months to a year of stronglifts you can go and do training for hypertrophy (size).
I'm guessing you're still a teenager, that includes 17, 18, 19. If so then the above advice will work. Get your bodyweight in lbs and multiply by between 20-24 inclusive. Then get a proper full body routine like stronglifts, you will get big and extremely strong with this, but if like me your goal is size then drop stronglifts after 6 months to 1 year. None of your bigger friends will be able to match your strength or size after doing SL 5x5 and eating properly.
http://stronglifts.com/stronglifts-5...ining-program/ is the link, but remember we are all unique and the 5000 calories is just a guess on his part. Definitely make sure you are eating more than 3000 calories. There is a lot of research that suggests that 6 meals per day and 3 meals per day will do much the same for you. But to hit my caloric targets I'd have to have 3 big meals, lunch would be impossible for me at school, therefore I eat 6 smallish meals per day.
Edit: Get your bodyweight in lbs, then eat 1g of protein/lb bw. I get about 1.7g per lb myself but that's just because of how much I eat.
