Take him to a doctor now because it could get worse

Well he is too young for prune juice. I would use Karol syrup just a 1/2 of table spoon in one of his bottles. Also, pushing his leg gently to his belly may relieve some gas.

give him some gas medicine and wait till tomorrow to see if he poos if not call his doc.

I had a similar problem…I spoke to a nurse and she told me to put her in a warm bath especially when it looks like she's trying to poop, supposedly it helps relax the muscles and tissue, then when she's trying to push it out to hold her against me in a way that her knees are up (sort of in a squating position) which also helps……but once it has been 3-4 days I would consider going to the doctor and have them help, they can put some medicine in his butt to make it easier for the baby to go to the bathroom. I know it's common for babies on formula to go some days without pooping, but I'm not sure how common it is in babies who are breastfed.

Breastfed babies can go a few days without pooping if he isn't fussy then I wouldn't worry about it. Babies grunt alot so it's hard to say if its b/c they are trying to go. Constipation in a breastfed baby is not too common.

try a bit of mineral oil in his bottle – less than 1/2 teaspoon
it is clear, odorless and tasteless, and your baby will be having some "smooth moves" real soon

try 1 teaspoon of corn syrup. feed it to him on your finger a couple of times a day until he goes.

You could take a sliver a soap….wet, and rub around and just inside the rectum to help loosen the stool, or give him some diluted prune juice, he isn't too young. I did that with both my children and it worked wonderfully. But also, breastfed babies, poop alot less then bottle fed babies. If he doesn't improve take him to the doctors.

My niece is having that same problem, try a little syrup (the clear one not sure what the name of it is) with about 2-3 ounces of warm water.
I am Hispanic and my mother would make us a tea from this plant called manzanilla. It also helps them fall asleep.
Good luck

Any kind of boiled herbs like tea will help.