Look into Tabata interval training for cardio. Maybe once a week. And on days you aren't recovering go for a lengthy run (mileage). Just don't forget to recover the day after a long or intense run.

Also, be aware of overtraining. Seeing as you stated that you are a kid, kids tend to do more sets then necisary. You don't actually gain more muscle overtraining, you instead tend not to repair muscle as well which greatly affects muscle growth. On major muscle groups such as the chest, back, shoul...