I agree with pps, the new formula may be causing constipation. This is normal. It will take him some days to adjust.
I wouldn't worry if it has been only one day from his last BM. Sometimes, my LO has BM every 3rd day, and the ped told me it was ok. He told me that if he was not uncomfortable or in pain, then that I shouldn't worry.
So just watch him closely to check that he is ok and with no discomfort.
Hugs and hope he is better now