How to beat performance plateau?

Hello people kk heres what i need. Im 16 years old. Im not really trying to lose weight but get more of a muscle tone. Im fairly skinny but not like super scrawny ima athletic build. Dont wana gain like mive muscle ya know just want some decent abs biceps triceps pecs ya know basically just to be in good shape. i run about 2 miles a day. im pretty sure iv hit plateau cause for the past 2 months havent really seen any difference from my current shape. was wondering if anyone has any idea how to break this. i heard i should try more challenging excersizes, but i cant afford to get a gym membership or buy my own gym lol. iv been relying on good old regular push ups sit ups crunches the running. got a pair of 10 lbs dumbells i use. thats about it. so yea any help would be really great thanks =)