Okay, this is something I didn't understand until after high school (regrettably). High school guys will pick on skinny or unathletic kids, and distance runners typically fall into the former group. If you're a freshman, unless you're running 16's or better for 5k (maybe 17's), you should be worried about your "coolness" rather than your times. That doesn't mean don't train hard, but seriously hit the gym, drink some protein (don't know about creatine at your age), then hit the f***ing gym again. If you are one of those sunken chest runners you will need to put on at least 20-30 pounds, maybe more. Do this until junior year, then you will have established yourself as a badass and no one will give a shit once you drop the weight and your times will start dropping too.
But seriously, you need to create an image for yourself by the time you get back to school in 4 months. I was a pretty mediocre runner in high school, since I got to college I literally more than doubled my bench press max (I maxed out at 115 in high school so that wasn't so hard). I put on a lot of weight but am not fat, I just look "athletic." I was a total wimp in high school, but if I had the body I do now I know no one would have given me any shit. Especially high schoolers, when I see the guys from my hs football team now, I know I could kick 3/4 of their asses (based on size/strength...maybe they know some jiu jitsu shit). Seriously, you can be the "big guy" on the cross country team for a year or two, not only will your teammates lay off you, but if you are putting up serious weight in the weight room then you'll definitely get respect from the other athletes too. PS, no one cares how many crunches you can do.
Oh, and the girls may actually notice you too. No one cares about the wimpy runner getting bullied about (don't mean to offend anyone, that was me too).