Why is this happening! HELP?

ok if you read my previus ques. you will know what im coming from! okkae so ova the summer before my first year in highskool i wanted to lose 25 pounds cuz im 14 yrs old 5'7 and 170-185 pounds and over the summer i druk nothing but water ate vegges ad fuit and grilled stuff after summer i loss the total of 14 pounds! i was so happy but i gradually started gaining the weight back towards the end cuz we went out of town alot before skool and it was hard to maintain my diet arond good foods yes i know its myu fault so now ive gained at least 12 pounds bak and fast and idk how in 4 weeks? but anways ive started playing vball rec league and ive lost three pounds without food dieting so for the past two weeks ive maintained tht weight but im not losing or gaining!!! so what can i do to start losing weight again because i woud like to lose 20 pounds by christmas! so please help me figure out a diet or calorie intake and exercise plan and keep in mind tht i eat lunch at school! thanks :)