Hello baby 1.5 months old, constipation, hasn't gone potty for three d…

Hello baby 1.5 months old, constipation, hasn't gone potty for three days. He is constipated, crying, how can I help him? He spits up slowly but can't go to the bathroom. What did you do? The doctor says it's normal for up to 7 days, but he is suffering, it hurts to watch.