Low testosterone

I have low testosterone but never realized until after my 20years i don't have beard, i feal depressed because almost all my friends have and even my junior once, then i went to a doctor , after he examined me, i have low testosterone , and he prescribed me a testosterone injection , and up to know my testosterone is not normal, during erection i have no sperm or low sperm. I want you to help me have a proper testosterone level, and that issue of low sperm count.