Nocturnal enuresis. Primary nocturnal enuresis, describes bedwetting from birth. There is often a genetic component, especially if one or both parents were bed-wetters. Causes include: small functional bladder capacity, abnormal "circadian rhythm" (producing more urine at night compared to day, less likely a neurologic or anatomic cause. 1st 2 r treatable with medication. Suggest consult with a urologist.
No short answer. This is called "nocturnal enuresis", and it can have several causes....Endocrine, urologic, nephrologic, psychogenic, etc..Best to see your family doc for a check-up....And possible referral to specialist if no obvious cause found..