Thank you for your query,
Newborns will reduce thier birth in first 10 days of life due to loss of excessive body fluid and inadequate feeds in the first week.
By the 2nd week they gain the birthweight
from there onwards they grow 25 to 30 grams per day till the age of 3 months.
Passing frequent and plenty of urination in neonatal period and in early infancy is a good sign and indicative of adequate feeding.
His stool pattern is also normal.
As his urine output is good, at present he is gaining weight, and sleeping for 3 hours after feeds. So these are suggestive of your breastfeeding
is sufficient for him and nothing to worry.
Hope I have answered your query.