Is it normal for a 4 month old BB to be peeing lesser n not poo for a day despite usual milk volume intake?

Peeing lesser i'm not sure but some babies experience constipation. My baby constipated for 4 days and only poo on 5th when she was about 3mths old. Pd said it is normal for bf babies. If you are concerned, see pd, trust ur mummy's instincts.