Welcome to HealthcareMagic. What you seem to be having is called micropenis or microphallus. It can be due to testosterone deficiency
, pituitary hormone deficiency
, hypergonadotropic hypogonadism
and growth hormone deficiency
. Various investigations required are chromosomal studies, hormone studies like Gonadotropins (LH and FSH), Testosterone and DHT levels, thyroid hormone levels, ultrasonography and testosterone therapy. Please get these investigations done. Treatment will depend on diagnosis. Hope it helps you. Regards.