Gym Advisor

alright, im currently 15 years old and i need some muscle growth
arm muscle that is… my BMI is 19.3… i got around 3 weeks before school starts and i need something to show

i do some cardio.. 100 crunches and run on treadmill 20 mins for a total amount of 2-2.5 miles a day … pushups i do around 50-100

any idea’s ? also could u tell me what to eat with the workout plan ? is milk good to drink after ?

Every time I excersize on my treadmill, I feel a pain in my right rib area. I only feel it after like 10 minutes on a good workout, but then it goes away after about a minute. I have no idea what this may be, maybe everyone has it, I dunno :S.