Guys never notice me. Why?

I've never been accepted on a date. Now its not like I sit on my butt all day waiting, I do try. Like I get to know guys and once I feel like I may have a chance and they could like me, I ask them if they would like to do something over the weekend or w e. But no guy has ever said yes or no guy has ever asked me on a date. Now I know that everyone faces rejection a lot but I'm kinda getting tired of it. I do try every single day of looking my best (brush teeth, shower, straighten hair, make up, cute outfits, awesome shoes, and if needed I would exercise if I was gaining weight) but no guy notices me. I do have some guy friend but they always come up to me not because there interested in me but because they want advice on how to approach one of my chick friends. I don't get what is wrong with me, maybe I'm ugly? maybe I'm too boring to hang with? or embarrassing to be seen with? I have no idea why a guy hasn't been interested. Another thing is I feel like giving up on the whole dating and just skip to the sex because I know a guy who is interested in only having sex with me. I feel like the only thing I could ever do with a guy is a one night stand and then leave. Please help?
Guys never notice me. Why?
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