Hiya,
We were worried recently that our LO was constipated - however now I'm not sure that she is. We thought she was because she stopped going once a day and started going every 2 days. That and her poo started to become a little firmer - though still squishy (sorry tmi) but reading up on it, she doesn't really fit the "symptoms" of constipation apart from crying when she poos - which she has done on and off since birth.
I was also told about a little sugar in cooled boiled water but other remedies I've read/been told about are;
Moving babies legs in the bicycle motion and gently massaging their tummies in a clockwise direction (supposed to help it pass through the intestine).
Just upping their water intake by giving a little water between feeds.
Putting a tsp of either prune, apple or pear juice in their feeds.
Putting vaseline on their rectum and/or gently massaging it with a cotton bud.
I unfortunately cannot tell you if these are particularly successful though, as I haven't tried them myself yet - sorry!