Yeah its bothersom. I had the same problem. Mainly because I didnt ever notice anyone looking. I am now 22 and married (to my first bf and only ever)....All I can say is it will happen when you least expect it and you have admirers you just dont know about. Trust me you do. I was just like you, never thought anyone even noticed me. But now when I looke back I remember somethings guys did for me and they normally wouldnt have if they didnt like me on some level. I even now figured out some of them were flirting (alot) and never knew it, I thought they were just being nice...stupid niave me. Just know there maybe someone you have no idea about who has a crush on you (just like you may have a crush on someone and they dont know). The older you get (next few years, maybe even months) you will get to where you wont care and just start flirting or flirting back with guys and they will take notice...for some reason guys like girls who flirt or at least seem interested (not telling you to go out and be flirty) its just sometimes you gotta take a chance and take charge (but when your ready of course)
Hope something helped ya out in all that rambling.
Amanda