I highlighted my hair twice, And my hair isn't as thick as normal, What can i use to help it get back?

In june I highlighted a little, And like 2 months ago I highlighted it a little more than last time, and Im 13 years old, with thick brown curly hair, and It hasn't been as thick, and its worrying me a lot, Im using Tresemme shampoo and conditioner, just the recovering one. the bottles are white and black. My hair dresser told me to use that its best. So I am and I feel like its not getting a thicker. And I don't like my hair being this medium thick. (: Help me!!! What can I use...