My hair is dry & damaged!?!?

So i used to have (naturally) thick wavy hair, in 8th grade I thinned it (somewhat alot) because it was unmanageable & super frizzy...but anyways, I had started using a flat iron almost everyday cus I hated my natural hair, and I still do cus Idk how im supposed to style my hair without frizzy hair popping out or anything so I feel like there's no hope..& my hair is falling out, it's literally fried & super THIN! idk what to do! Help!?!