Weight Loss Motivation

Hi I'm 16 and going into my junior year, I've always been overweight since like 3rd grade but conscious about my weight even as a kindergartener. Point is I'm really trying to lose weight but I always lose my motivation or I get lazy a week in and it's killing me. It's usually the food i eat, I think I'm actually addicted to junk food. I declared that I would lose the weight (5 pounds every month) before junior ring dance and finally be able to wear a dress without being insecure about my tummy, legs, back fat, and arms. I don't feel comfortable in the gym either but I'll try to go in and not think about others, this is for me...can I please have some advice? Fyi I'm currently 169.8 pounds and 5'3" and my goal is to hit 120-130