My hair isn't thinning but is thin: full head of hair and it isn't falling out. How can I get thick and healthy? (photo)

Hello , i have a full head of hair however it is thin at the roots naturally, it isnt thinning but is thin. If i grow my hair out the top ends are thick and full but i can tell the bottom half near the roots is thin, how can i fix this? Would i require surgery or is a certain hair treatment such as special shampoos help? My genetics might not be the issue as my dad and grandpa still have a full head of hair. I am only 21 and it is hurting my confidence level. Thanks i have provided a picture

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