I am 22 years old and thinning all over my head. What should I do?

You need to bet both a miniaturization study and a HAIRCHECK test by a doctor who knows these modalities and can help you with the diagnosis you need. The miniaturization study will look at the back of your head (donor area) and if you are miniaturizing there, they you have DUPA (Diffuse Unpatterned Alopecia) which is a far more grave prognosis that standard genetic balding for men.