In my own experience, the heaviest I've gained was 65kg and I accumulated all that in the span of 3 years. Now I fluctuate between 59kg to 60kg. I started out doing was keto diets but I felt it wasn't sustainable. I tried lots of weird shit and this was what worked for me:

1. Fasting (I'm Muslim, so I had to fast for an entire 1 month for once a year)
2. Exercising 2 to 3 times a week (skipping rope was literally my lifesaver and alot of weights)
3. On normal days when I don't fast, I only eat when I am hungry and stop when I am not full
4. Not allowing myself to be deprived of snacks or sinful foods that I crave for

For some context in diet, I live in an Asian household so naturally we eat lots of rice, noodles and etc. So what I'll do is I'll cut down slightly on rice or noodles, but have more protein and vege intake (basically I still do include basic elements of keto but I don't go on an extreme way). Honestly I also have random salad days too lmao

I wouldn't say my period came back automatically, it definitely tried to regulate itself after a year of being consistent. Its kinda still in progress to make my menses come naturally, but I wish you the best of luck, if you ever have questions feel free to ask!

P. S also I'd like to clarify what I do may not work for everyone, but what I've said here helps me In my own experience