I started feeding my five-month-old son solid food three weeks ago. During the first week, he did not have a bowel movement until after six days. The consistency of his stool was thick but still soft. I have continued to feed him solid food, and again he has not had a bowel movement for five days now.
Is this normal? Should I be doing something different?
It's fairly common to see a change in stool patterns when an infant has had a change in diet. Adding solids adds indigestible bulk within the intestine, which will thicken the stool and can decrease its frequency. That doesn't necessarily mean there is a problem.
'Constipation' in infants is defined more by the consistency of the stools than by their frequency. An infant who passes fully-formed stool or rock hard 'pebbles' is a constipated one.
If your son is happy, eating well and passing soft stools on a reasonably regular basis (beyond five or six days is concerning) then there isn't anything you would need to do differently at this stage beyond making sure he has plenty of liquid in his diet.