Why do I have such low self esteem and lack confidence? Why can't I just be thankful and not dwell on what doe?

Idk what's wrong with me. I try so hard to make appearances, to look good and I spend considerable amounts of time perking myself up before parties, outings, and even school. I build myself up, and then later in the day, I always feel like ****. Why? I broke up with my bf of three years to be single and I feel more miserable than when I was going thru the whole i love you but im not in love with you stage. Now I'm single and in college and I can't find anyone who wants to get to know me on a substantial level, which is defiantly what I want and what I deem important. Can someone please give insight on how to feel better about oneself and to build confidence even if the environment itself is pressure-filled and fake? I feel like I have so much to offer, beauty and brains but no one even cares and Idk what to do with myself, I wish I thought like a guy and ****** every guy I wanted but I'm a chick, and I just want some genuineness in my life.