A change in formula can cause constipation and adding solids too and also again when he's weened and begins drinking whole milk. However, IT IS NOT NORMAL for them to miss a day of pooping. Babies or anyone going a day or days without pooping is taxing on the body. The colon gets rid of wastes and passes toxins out of your body that have been filtered out of the liver and other organs. If you don't poop the toxins build up in your system and toxify your body and blood stream. Have you ever got nauseated because you haven't pooped in a day or two? That's why. You can also die from not pooping in 5 or more days. Please don't anyone let it go on that long.
I would not use laxatives or other medicines. Try a little carrot juice in his formula. It has an elimination effect. It still helps my son and he's 1 year and 9 months old. I heard of adding prune juice also but have never needed to try it.
Adults can also use the carrot juice or take fiber such as ground flax seed, ground pee hull fiber, chia seed, alfalfa whole leaf, barley whole leaf. If you take too much fiber, these too can possibly cause constipation. Check at a health food store. Do not use psyllium. It is extremely harsh on your system and clogs you up. Drink lots and lots of water, eat raw veggies and fruit---these have natural elimination effects.
Things that cause anyone to be constipated are: dairy (milk and cheese, yogurt, etc...) bread (wheat---anything with wheat like cookies and some pasta), calcium supplements and for some dried fruit.
I've had 18 years experience with my own constipation problems and with lots of research of what to eat and not eat (the causes and why) while omitting and adding these things to my diet I've found the above are some causes and cures. Babies are extremely more sensitive than us adults.
I hope this helps.
K.