Im 15 &i eat alot I have extra meals &i eat alot of calories but Im still skinny, how can I becom?

Im a semi-pro Kick Boxer, trust me when I say over-eating is the biggest cause of an unhealthy body! Stop stuffing yourself full and form a strict diet plan to achieve your goal. You should have a balanced breakfast, I recommend you to start having weetabix with full-fat milk (2 biscuits of weetabix). Be sure to eat something every 4 hours but do not binge on chocolate or crisps, fruit or veggies should suffice. For lunch you should have anything you like except fast food, and dinner should be similar. The reason why its harder to gain weight at your age is due to your metabolism or worms in your tummy, you can de-worm yourself after seeing a doctor or chemist. Work out properly, if you use an I-phone download the Adrain James app and follow it 3 times a week, or if your on youtube a lot then follow Leslie Sansone's 3 mile workouts, if those are too easy then try Denise Austins workouts. At 15 you should not lift weights as that will stunt your growth. Good luck!