Here is another thought that you reminded me of when you mentioned skinny < size 14. What is your bone size? If you are not sure, take your right hand and try to touch the thumb and middle finger around your left wrist, the narrowest spot. If they touch easily, you are small boned. If they just touch, you are medium boned. If you cannot touch them together, you are large boned like I am. I could not be a size 14 without question being drawn to my health, if I'm lucky I can get down to a 16, which to me would be just fine. I personally don't put much stock into clothing size = skinniness since alot depends on the cut and the manufacturer as opposed to some kind of universal standard.
Always remember as well, most fast food places do have healthier alternatives. Or modify your condiments. Getting a burger? No Mayo. Taco Bell? try their Fresca meals and get the chicken instead of the beef. Chinese food? go with a vegetarian or chicken dish that doesn't have a lot of sauce (and no sweet & sour chicken!) or something like the sauteed green beans. Also most fast food have those menu nutrition guides, either as handout or online. Take a quick look at those and figure out a plan if you do feel the need to resort to fast food. Want a nuk'em meal? Try Lean Cuisine (their Paninis are pretty good). Stay away from deep fried and if deep fried is all the place offers, get sides like salad, coleslaw or whatever.
You CAN do it! Don't give up!
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.