Why do guys friendzone me??

Just to give a little background, I'm 19, in college, not a virgin. I have a lot of guy friends, but I've never had a boyfriend. As soon as I meet someone I feel like I'm immediately in the friendzone, there's never any flirting, the energy is either like we've known each other for 10 years or he's my brother. Any attempt by me at flirting or hitting on someone is just shut down. I'm so confused as to why guys have zero interest in me beyond exclusively sex or exclusively friendship. Am I not pretty enough? Am I not interesting enough? Everyone always says "you're trying too hard," but when I get upset over not having a boyfriend they say "are you even trying?" I'm just so confused and tired of being single at this point. I feel defective because nobody wants me. I feel lonely because my girl friends don't care, and I can't discuss it with my guy friends because it would basically announce "I was interested in you at one point." I'm just so scared of missing out on love, and I don't know what I'm supposed to do differently to find it.