Ive lost weight, but i want to lose MORE?

hi there. im 15 years old and in april i weighed 187 pounds but now (June 11th) i weight 167. so ive lost 20 pounds, but i feel like i should and could do more. my long term goal is 135 pounds. i want to be an actress, and ive always felt that its hard to be a sucesfull obese actress. so i kicked it into gear and got a gym membership and started eating less. but now im less motivated and going back to my old lazy ways and its almost summer! how can i keep losing weight? i really dont care how long it takes, as long as i do it the healty way and kep it off. i do not want diets because i believe weightloss should be a self earned accomplishment. thank you!:)