How to get my hair thick again

heyy,

so i am 23 years old and female. And I used to have really thick hair. Now my hair has thinned to 1/3 or its original volume. I am terriffied really. its been over 3-4 years when it stared getting thinner. Can i get them back to thick again? What can I do? now my hair is to most people seen as normal thickness to slightly thick. i have no bald spots or anything. My hair started thinning in the front more. and I notice i loose a lot of hair. What should I do??