Mesotherapy for hair thinning or any other technique or serum which is effective for hair thinning?

I am a 21 old male and lately I have been experiencing hair thinning. My hair was always thin as I remember and I do not see any obvious hair loss but my hair seems thinner and weaker. First, how can I be sure that I am experiencing hair thinning? What could cause this thinning if there is one? And also I heard mesotherapy for hair. Is it effective or proven ? If not are there any other methods or serums for cure or are there any trustable tests to find out if I really have hair thinning ?