I want a nice body. help pease!!?

OK. i'm VERY skinny ( not anterestic skinny or now u see me now u don't when i turn side ways) but i want to gain wait... im 100lbs. I really wanna gain weight not only beacuase I'm tired of hearing "ur so skinny" and " u so thin"but i wanna feel "sexier". I'm writing this to find out how to gain HEALTHY weight and look good in 3 months. please help me!! =O