your doctor is thinking about a rare condition known as a 'patent urachus' or a 'urachal cyst'.
This is a fine biological duct or a fluid-filled swelling between the top of the bladder and the belly button (the umbilicus
The duct has a function in the embryo but then normally closes-up to become a mere ligament, which is an empty cord of scar-like tissue.
Very rarely it does not heal and can present later in life as a swelling, perhaps discharging urine or mucus from a cyst within an open (patent) urachus.
However, it is rare and there are other more common conditions that can cause persistent discharges from the belly button like a mixed fungal and bacterial infection.
Get the culture of discharge done and take the medicines accordingly.
is very common at belly button as this is a moist and humid area,which is ideal for fungal growth.