Girls, baby is not pooping at 1.5 months old, what should I do? After …

Girls, baby is not pooping at 1.5 months old, what should I do? After 3 days, the baby cries and fusses, he's restless. On day 7, I give him Microlax. The pediatrician said that it can happen in babies up to 3 months old, she recommended Microlax. Who had this experience? The baby is 3 months old soon. I'm already tired all day long just holding him, if he falls asleep, I try to put him down, he wakes up and cries, on his arms he sleeps a little bit. How to be??