Why don't guys like me?

I have no idea why I have so many problems with guys. Like even as just friends they tend to not want to be friends anymore after several months past. They normally don't want to be friends because I'm not cool anymore or they don't get their way, like sometimes they want to start FWB with me but I always say no.Thats what happend with two of my old guy friends. In dating or relationships I've never been concidered girlfriend material. I've never been asked out anywhere with a guy. I have no idea what guys are thinking because I think that I am pretty and a cool person. I just don't get why guys are friends then they don't want to be friends. Or why guys never seem to ask me to spend time with them. I'm 16 turning 17 with two more years in high school. Its scarying me now because it never seems to work with me and guys. Please help