3 weeks 2 days baby boy having trouble pooping

FTM need help! My son has not pooped. Yesterday he had no bowel movement and none today yet. I took him to the pediatrician and they said if he doesnt poop by today to give him a suppository they prescribed. He has a lot of gas like you can actually hear it and feel when touching his belly. He gets red and clinches his fist and while asleep he moves from trying to push so hard. He is breastfeeding and formula feed aswell. Do you moms have any remedies that can help him poop before i try the suppository i feel like it will hurt his little rectum because he's so small