Please tell me How to gain weight ?

hey im 5ft7 and i weigh 115. I really wana gain more weight cus my legs and arms are scrawny and i barely have a but! no matter how much i eat nothings happening!!!! why is that happening !!? i eat 5 times a day and sometimes i lick er in hope of getting a flirtacious round backside like my friends. is something wrong with me?!!!!