I'm a freshman in HS, in 8th grade I hit 2:09 in an 800m. The highschool coach wanted me to run Cross Country this year, But I am doing really shit because I always get a sideache in any sort of races or hard runs my times are still improving, but haven't had a single race where I don't get a sideache, yesterday I got 19:31 in a 5k on a reasonable course, but I need some advice on preventing side aches. My coach has helped me try everything, hes given me a special warm up, and our team already does core everyday and I try my hardest in that. So i'm stuck. Really disappointed because I was really looking to break 19:00 This year... Help would be appreciated.