How to make my hair grow ?

so since 3rd grade i've been in cheerleading , ballet , gymnastics , dance , and a lot of sports that require me to slick my hair back in a ponytail with a lot of hair spray and now that I'm out of HS i've noticed that i have bald spots on the side of my head by my ears they're really big and noticable and my hair is really thin and dry my mom says that maybe the hairspray burned my roots and that's why it's not growing back . what can i do/use to get my hair growing again ?