How can i get boys attention?

i am not the prettiest thing around. i am thick, i have a birthmark on my face and i just feel ugly. it always seems as if all of my friends have boyfriends or someone has a crush on them. i am homeschooled so i can understand not having and guy friends but it seems everywhere i go boys just avoid me. and the only time a guy ever had a crush on me was because he liked my rack. i just feel really ugly and my big sister always makes comments about me being thick and musclar. what can i do to slim down and become more attractive.