How to stop brother from making fun of me?

He always makes fun of me, it could be when were alone or in front of a group of people. He always calls me fat, yes i am a little bit overweight but not much. He's the one who eats like a maniac and i don't even eat alot and i eat healthier. I am a junior and he is a senior in high school. All his friends went to our school and none of my friends did and i had no one. He always says i have no friends. Also i am 16 and barely starting puberty. I dont even have armpit hair yet and its pretty embarrassing and he will say this infront of people at school, guys and girls both and whenever i say something he will always say something about my balls needing to drop. And he always gets set up with hot girls, whether its parent friendships (everyone of our family friends always happen to be hot and be his age) or whether his friends set him up with someone, and he thinks he is soooo cool. I don't mean to be a whiny little ***** but i am so fed up! He gets everything hand fed to him and he takes all the credit and he always makes me feel like a loser. We fight sometimes but he wins 99% of the time cuz im still small and my muscles havent developed much, even with 5 gym trips a week.