hi, thank you for your query. i think most probably you re experiencing 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. other common causes can be- -lump in the belly button -infection i would advise you to consult a GP,who will take a sample of the fluid and send it for analysis and also do a complete physical examination to rule out other causes.if confirmed the cyst can be fixed with surgery. thank you, wishing you good health