My hair is thinning?

I am 26 years old and as a child and teen I had very thick hair and when I was a lot younger would sometimes even have to have the beautician thin it some during regular cuts. Lately I've noticed that it seems like my hair is getting really thin. Especially around the crown of my scalp and a little down towards the back. I have always kept my hair long and taken care of it as best as I know how so this is really starting to worry me. I haven't noticed any balding places or that I am losing an unnatural amount of hair. Just wondering if anyone else around my age has experienced this or if anyone has some advice on what I may can do to help regain some thickness and prevent it from thinning any more. Thank you!