Genetic female hairloss, or Androgenic/Androgenetic Alopecia ("AGA"), can start in your teens. But it usually happens gradually. To go from super-thick to noticeably thinning in two years is not typical for that type of loss. However, AGA loss is usually the worst at the crown, like yours. AGA can be stalled for some women with Rogaine or prescription anti-androgen medications.

Thyroid problems, extreme iron deficiency (it has to be pretty bad), birth control, PCOS, and very high levels of stress can cause faster types of hair loss. These can often be reversed. I strongly suggest going to a doctor to have those issues ruled out.

Are you sure there are not any circular patches of loss? This would be Alopecia Areata, which is an immune disorder that can go into remission.

I have AGA, and my hair started thinning at puberty. It got really bad when I was in grad school the last couple of years because I lost extra hair due to stress.

If your hair loss is permanent, there are lots of things you can do. I've rocked some hot wigs this year. It was fun having thick hair again, but I couldn't help feeling self-conscious; I've gone back to my pixie "combover" for now (ugh). If the top of your hair gets bad but the rest stays thick, you can use hair powder to conceal the thinning; you can also use a topper, which is a partial hairpiece that fastens to the top of your head. It's like extensions but isn't sewn in. Some women shave it off (tried that--my head has a shark's fin on top and it's not a good look), and some women just wear their thin hair and don't worry about it.

I've done a lot of research on this and I know how miserable the whole experience can make you. Worrying about what will happen next and what your hair will look like in the future seems to be a normal stage in the process. Unfortunately, so is trying every supplement and product you can buy. A good doctor can save you a lot of time and money.

I'm sorry you have to deal with this so young. Feel free to PM me! There are some great support forums for women with hair loss. You're not alone in facing this. Hope you find some answers!