Congrats on your bub! smile
Constipation is all about the consistency of the poo, so your bub definitely isn't constipated smile
As pp have said, I do remember mine getting very distressed before pooing in the early days- getting used to the new sensations, I guess.
You could have a look at his anus, see if maybe it's red or irritated? Other than that, give your health nurse a ring, or if you're really concerned, take him for a check-up.
Good luck and enjoy your new addition smile