Why cant i ever tell a boy yes?

Ok well no matter how much I like a boy I can't ever say yes when they ask me out or ask if I like them evn if they tell me they like me I dnt knw why I feel like they're just joking or something so I always say no how can I get over this and why am I like this btw I'm 14 and lke everyone has hd a bf or gf I'm not ugly boys have told me I'm pretty and y and I flirt wit boys but say no one boy asked me if I liked girls n I dnt lol but what should I do?