Constipation?

My new born is just a week and a day old, he  is formula fed with gerber good start, he has been pooping great! 3-4 times a day and good color. However it has now since been2 days since he past his last stool, he is vey gassy though and farts a lot and I can tell he's pushing to possibly relieve a stool but then gets REALLY fussy. Any suggestions on how to relieve? Should I try a new formula maybe? HELP it breaks my heart to think my baby is in pain from not being able to poo🙈😔