My son routinely goes every 3 days. That just started a few weeks ago. When he goes longer than that, my pediatrician recommended getting a qtip with some Vaseline on it and rubbing it around his anus. Worked like a charm when we needed it to. Call your dr to see what he/she recommends.
My little one goes every few days and she even went 10 days without going once. The doc said at 10 days to bring her in. They aren't concerned as long as they go once a week. If he is exclusively bf then it is fine because they are super efficient at using all the goodies in the milk, there just isn't any waste left over.
Re: Changes in babies