I'm guessing since you're 14 that you're still in a gym class a few times a week at school. If you really try hard in your gym class you can be burning a ton of calories (depending on what you are doing in class), which could be one of the reasons why you can eat a ton and not gain any weight. I was in the same boat in high school (I was around 6' 3" and 135 lbs to 150 lbs.)
But being as you're so young, I would highly recommend what a few others have said, and that is to practice your technique and get it down now and worry about weights in a year or so. If you want to get stronger, do body weight exercises (such as pushups, body-weight squats, etc.). I've read articles about how lifting weights too heavily when you're that young can screw up your body and I've read articles that said it won't (I used to work with somebody who said he was flat footed because he lifted too much weight too young while his body was still growing).
If you still want to add mass, then I'd suggest protein shakes and possibly the supplements that are mass gainers (I don't know their real name). Also, to pack on the calories (since you need more calories than your body uses to maintain itself in order to gain muscle) I'd recommend getting some of the drinks that people trying to lose weight use (I currently have Boost) but instead of using it as a meal, drink it in between meals. The one I have is around 320 calories per serving and it's around 8 oz. so just 1 to 3 on top of what you already eat should help with that.