M.M.
Do not panic right now... Whenever you are changing formulas, it takes about a week for the systems to regulate. We actually do not consider babies to be constipated unless it has been over a week, they are having hard poops or showing other signs of GI distress. New parents become "Poop Patrolers" lol and it is actually more of a problem for them than the baby many times. Please do not follow the juice idea. It will be fine. You can do a rectal temp with a little lubricant and it usually works if the baby needs to go. When parents take my newborn class and I tell them to stop poop worrying; when they come back with the toddlers years lady they say it is one of the best advice they had been given. Good luck and Congratulations.