I am 16 and I weigh about 256 at 6' feet. And I would like to lose 20 pounds?

I am sixteen years old and I weigh 256 pounds at 6' feet tall. And I would like to lose 25-30 pounds by the end of the summer. At the beginning of this school year I weighed 238 pounds and was much happier. I did not change my lifestyle and still I gained dramatically in the course of one year. I live in VT so I am pretty active and outdoorsy. I play Paintball on the weekends and during the week I work outside. I can lose weight and have lost a lot before but I always gain it back really fast and seemingly arbitrarily seeming as I am outdoors and active a lot. But lately I feel that the extra weight is bogging me down more than ever And I would like to lose that stubborn 25-30 pounds that just won't stay off. The rest of my family is also fat but seeing as I am always active and don't eat excessively it doesn't make sense that I am too. Please help.