I was in your situation about 2 years ago towards the end of my junior year in high school I had been lifting since the begining of the year and had got cutter but not bigger and hadn't made any signifigant muscle gain. The secret like what has already been stated is your diet. Get on a good multi vitaman, i recomend gnc mega men, also you have to increase your protien intake which means trying to eat 6 small meals a day and taking protien. I usually took liquid amino acids about an hour before workout, about an hour after workout i'd take protien, and before i went to sleep i'd take protien. But if you are like me and wanted to see real results, I'd recomend getting on NO2. Read up about NO2 here:
http://www.getno2.com/ its pretty expensive but it works, after 2 21 day cycles (The bottles last 21 days) you will be seeing serious results. Taking NO2, protien, and having the right diet and most importantly a good workout routine will enable you to make signifigant gains. But now that I'm at the citadel now I can't afford 60 bucks a month for no2 so i'm not on it anymore, once i'm finished with knob year though I plan on getting back on it, trust me it works, it may be a little expensive but if you wanna get ripped its worth it.