Most babies experience constipation when moving to a higher stage.
This is due to the increase in iron. This problem occurs when there is a sudden transition or an improper diet. There are easy solutions to constipation. Please read How to Transition Between Stages and also explore Suggested Diet Plans. If the transition is gradual, it will help relieve constipation caused by higher stages. We recommend feeding porridge and purees to soften stool and induce regulation of bowel movements. Prune purees will definitely help. There are many prune purees available at local stores suitable from the 4th month.
If nothing works and it's been over 48 hours of constipation, then you may use a prior stage for an additional couple of weeks and try the higher stage later. Always consult with your pediatrician first.