Th problem isn't that you "switched too fast", it's that you were starving yourself to lose weight, and you are still undereating.
Please, listen when people tell you that what you are doing is dangerous.
You are still seriously under eating - losing your periods is a sure sign of this too. You can't maintain on 1,200 calories a day doing your level of exercise at 15 years of age - you need to FEED your growing ,developing body, otherwise you are going to do yourself permanent damage. If you find this hard to accept,please consider asking your doctor. All your threads show that you are under eating and yet you are not willing to accept advise on upping your calories.
At your age, and activity level, particularly in view of your missing period, you need 2,500+ calories a day to repair your poor body, repair your metabolism, and get your periods back.
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