Why am I sooooooo Skinny?

I am an 18 year old boy and have always been skinny and taken the piss out of me its sooo embarrisin and is probly one of the main reasons I can't get a nice girlfriend. Im not just talking any skinny here Im talking bones poking out my shoulders that you can see even wen wearing a t-shirt, tiny legs a 25inch waist and bony hands and feet and ankles, even girls weigh more than I do im such a tiny fragile weakling. I eat fine and live a healthy lifestyle im not anorexic but i am one of the skinniest people I actually know its soooo embarrisin and I know I can't get a girlfriend because of this they won't want a skinny weasel as their boyfriend :( help!!!!!