Your describing the hair I used to have. The only thing I can tell you is that I started experimenting with chemical jobs at that age, started with a mild coloring job, which went from blond -> dark brown. Now I also tried perming my hair and since then, my hair looked very nice, started to tangle less, wasn't oily any more, felt fine and was nice.
Still didn't get me a date, but I melted each time I saw the color or curls in the mirror.
So my hair type like it was back then was similar, but I got rid of it by overcoming my initial fear for coloring and perming. Talking to your hairdresser may help. But look for different ones until you find one that you like. I've had one that refused to cut just a little bit off with each visit because she thought I could never get good hair that grows past my shoulders, nor perm or color it. I had to keep it short. Rubbish, of course, but she thought the only good look would be short hair. I found a better hairdresser that comforted me and colored my hair while I was sitting at the mirror, so that I could see what happened.
While I don't visit her anymore either, it set me over my initial fear for chemical jobs and resulted into the hair I have today, which is way past shoulder length and while not being thick, it's good and healthy.