Nexplanon and weight gain

I need some advice. I’m about to get the nexplanon and all the comments people complain of weight gain. I’m currently at 170 and this is the biggest I’ve ever been and I don’t want to get bigger. I was an athlete in high school and still work out pretty regularly but my eating habits probably could use some work. Did you notice weight gain right away? If I really focus on working out and eating better, will I still gain lots of weight