Best Form of birth control?

I’m 15, I only have sex with one guy and only every couple of months so I want to go on birth control so I stop having panic attacks after every time I have sex.

My period’s are heavy too, I have unbearable cramps and they get worse every month.

I want to start birth control but I’ve heard with a lot of kinds you gain weight. I don’t want to gain any weight, I’ve been the same weight for years but recently it’s been easy for me to put weight on so I want something that won’t make me gain anymore aside from that. Please let me know. I have considered the patch but I would stress about it falling off in the shower too much. My mom said for her depo made her gain a lot of weight. And I don’t want to get the implant.