teen weight loss / fitness

hi! i'm 123lb, 5'3, and a female freshman who plays all three seasons sports (xc, winter track, & lax) i've recently gained weight over a couple of months (8lb from 115lb) and was wondering how to lose it again. not only that, i want to get more fit for sports in general to improve performance.

i'm starting to run daily again and currently have lax 6x a week. what exercises should i do and what should i eat? how did others do it?