What Causes Passage Of Milky Urine In Initial Urine Flow?

i am 28 years old male ,height 5.8 ,weight 70,medically fit in the past except i experience a painfull urine discharge a year back which possibally a small stone discharge through urine after that i consult a doctor who advise kidney scan for possible stone but no stone appeared in kidneys and i did not feel that kind of pain again also i observe in the past that sometimes rarely when i urinate ,a non-transparent urine or milky kind of urine initially while urinating but for a month i observe it almost daily one or two times a day.Also there is no pain and blood observed in the urine.plz tell me why it is happening and what should i do to cure it?thnks