Tryna lose weight

Hey guys just need some advice. I’m 16 years old, I weight about 160 and I wanna be about 140-145 by December because it’s my sisters wedding. I’ve always tried diets and everything but nothing seemed to work. Any advice??? Like literally anything would be appreciated. Also I’ve been breaking out a lot more recently. I would only break out on my forehead and now I’m breaking out on my cheeks. I need help!!!!!