Don't FRET! GhettoStudMuffin is HERE!
You're still young and from what I can tell you're probably 19-21.
That's means you're still not fully matured physically.
I'm 24 and weight 213-214lbs right now, but back in high school I could never get heavier than 168lbs no matter how much I ate. Just wouldn't happen.
By the time I was 20 my average bodyweight was 180lbs not even lifting. Now Im 24 and it's 200lbs when not lifting and it ain't all fat.
What I'm trying to say is that you will thicken up some more and put on some weight in the next 3-5 years and not all of it will be fat, but muscle and bone density.
You could put on 50lbs in a year naturally if you EAT like a madman, eating mostly good food, just HUGE quantities of it and lift like a madman 3-5 times a week and constantly strive to get stronger.
One thing I have see no one really talk about is SLEEP! Become a SLEEP FIEND! Sleep 9-10 hours every night, EAT like a madman, train like a madman 3-5 days a week and YOU WILL GROW FAST!
Believe in yourself. Gaining weight is EASY when you EAT ALOT and TRAIN HARD!