I don't know what kind of "extreme" exercise you have tried, but you could try some weight lifting. Joyce Vedral has some good books for women on the subject, as a place to learn the exercises, and the public library will have her books. Plus she has an encouraging attitude and has written books for teens. She became a bodybuilder in middle age. Anyway, if you do some intense weight lifting, like heavy enough that you can only do 5-10 repetitions before crapping out, then you will be building muscle. When you build muscle, as explained well in the popular book "Body for life" (also written by a very encouraging/inspiring type guy) then your hormones will change and you will be in fat burning mode. I have found these two authors helpful. They write for ordinary people, not athletes. I am not an athlete. I feel both these people have high integrity, although no need to buy the second guy's supplements. Both books also describe sensible eating plans - to support a good life and feel good, not to obsess about appearance. (Don't worry about Vedral's implants. Not important. It's something competitive bodybuilders do sometimes because they lose all the body fat and don't look like women any more. )

Try something new. It might help. I was about your weight in high school. I look back at photos and I see a rather beautiful young woman. Too bad I had no idea about that at the time. So try to make the most of what you have and go for it.