How to gain weight? will i get a "beer belly"?

i'm a 16 year old guy and i'm really skinny.... so i've been eating a ton lately and i don't seem to be gaining.... every day i fill myself till i'm nauseous and i don't gain anything.... i'm also afraid that if i keep eating like this that ill gain weight but only in my stomach.... i DON'T want to have a "beer" belly... and if i accidentally skip a day of eating i lose 5 pounds..... i just recently went to the doctor and nothings really wrong with me.... my sisters and brother have the same problem.... so i dont think its like a worm or any disease.......so are there certain foods to make your thighs and butt bigger? and also my elbos stick out really far... so i was thinking i need to get my biceps bigger? i do work out a little bit.... so my questions are... if i eat alot will i gain weight evenly? or will i get a beer belly?.... and are there foods that make certain parts of the body bigger? (ive heard KFC goes straight to your butt and thighs but i didn't know if that was true) so can someone help me please?