Hi & Welcome!
I used to teach JHS up north in Japan as an AET. Although I'm a little rusty on teaching kids, I'm sure I could come up with some solutions.
I'm surprised that they are shy, and don't want to learn English. At that age, especially the 1st and 2nd years, they love English. Are you sure they just aren't used to you yet? Are you sure that the previous AET wasn't a horrible person who made English a living nightmare?
Give it time, be persistent, and give the students every opportunity to talk with you. Hang out after school, and ask to participate in some of the club activities (or go to the gym during an off period and play volleyball, basketball, or whatever with the kids). This worked for me, and I soon had little trouble getting everyone to participate.