Birth control, arm implant

I’ll be 18 soon, and I need to get birth control mostly for better periods and less cramps (I have horrrrible cramps) but also of course for safer sex with my man. However, I’m worried about a lot of weight gain. Have you guys gained a lot of weight and it stick from the arm implant or was it just water retention and went away after a couple of months. I am not sure 100% but I tried doing my own research and I found most of it being water retention ect and that most weight gain from birth control is from the excessive hunger from estrogen and such. Just need some friendly advice, thankyou:)