Strategies To Lose Weight Fast

I currently weigh 108 pounds at the age of 15, i used to weigh 143 pounds but lost a lot of weight in a very short space of time, around 3 months. I ate very little and now i eat more however still very small amounts. I have been to doctors who say i am underweight and have a low bmi. However, my ankles are still big and i would really like to know how to lose weight on my ankles without having to eat 500 calories a day. Please help!

I am 5’2 1/2, and around 95 lbs. My upper body stays small no matter how much weight I gain (I never gain any in my stomach or ribcage area), but my legs are pretty disproportional to the rest of my body, and it makes it hard to find jeans with a small waist and bigger legs.
My question is what should my weight goal be?
I know I want to lose weight in my legs, but how much can I lose without being unhealthy?