I'm not gaining weight since grade school.

first off, welcome to mylot, zeith. try to eat more often during the day. and be conscious of what you eat. increase your protein and carb intake and be physically active. i myself am thin, so i probably know exactly how you feel. of course, all i'm saying is easier said than done. but that shouldn't stop you. also try to get your thyroid checked. ask your doctor how it affects your weight.

How tall are you? What is your ideal weight supposedly? I had the same problem when i was your age. I never gained weight, i'm 5'3 and at that time i was about the same weight as you and i was so skinny. It was not nice at all as i have a boyish frame. I really wanted to gain weight and i did everything including drinking protein milk, taking vitamins, etc. but still failed. It stayed that way even when i got pregnant. In fact my weight when i was pregnant was only 47kg which means i never gained weight and all the kilograms i gained were my babies weight. Until i discovered a secret which is not a secret anymore since i have shared this to many people. One important thing in dieting (whether it's gaining or losing weight) is discipline. If you don't have this, then my advise will never work at all. Believe me, when i did this, i gained a kilogram a week. What did i do? Here it is. I eat my meal almost at the same time everyday. Time is important as this would help you increase your appetite. Eat 5 times a day or more if you can and remember you should do this at exactly the same time everyday. I eat breakfast at 8am, i eat snacks by 10am, lunch at exactly 12 noon, healthy snacks by 3 or 4pm, and dinner at 7 or 8. If i stay up late which rarely happens, i eat snacks again by 10pm. Remember sleeping is important as well. When i was in this habit of gaining weight, i go to bed at 8pm watch a movie to make me sleepy and then fall asleep by 9 or 10pm. If you follow this program, you will gain weight as fast as i did. I'm happy at 53 kilograms now. In fact i was 55kg before but i had to lose the excess fat on my belly. Good luck.