My self esteem is so low. help?

i'll go out with anyone even if i know there just looking for sex. i have No friends or have ever had a real relationship. i just let myself go life stopped mattering i stopped trying to look nice. i used to have a happy go-lucky personality everyone loved me. i turned 13 that all changed my friends left me. you know how they say lucky 13. willl mine is UN-lucky 13