What can you do if baby doesn’t poo?

Recently, one of my friend’s baby at 3 months couldn’t poo for 5 days, thus, she was a bit worried. She asked around and asked if it’s normal. My doctor friend mentions it is quite normal and may even not poo for a week! The best solution is to let the baby drink prune juice! Guarantee can poo! Hahaha… Even suitable for adults! Do try it if someone suffers from constipation. But of course, there may be exceptions! :P