My son has been constipated since I was breastfeeding him. He has never had formula milk, so that was not the problem. He was really in pain whenever he had to poo, straining forever, with blood in faeces etc. It was torture for him and for us.
I tried every possible cure. I did not want to use laxatives regularly so I tried osteopathy, homoeopathy, chinese medicine, prune juice, olive oil, flax oil, drinking a lot of water, prunes, etc. Nothing. In the end I gave up and my paediatrician suggested at first a massive dose of Senakot and Lactulose (two tea spoons of Senakot a day and 4 tea spoons of Lactulose a day). I have been progressively reducing the dose in the last two years and now we are down to one tea spoon of Lactulose a day. He thinks that after a while babies associate pooing with pain and then they refuse to poo, so it becomes a vicious circle. He suggested that we made it really easy for him and then slowly reduce the doses. So far it has worked.
I will also try other suggestions that have been recommended by other mothers, since constipation is always at the back of my mind with my son and I feel the enemy is not beaten yet. Something that was not a medicine and really worked for us was kiwis. With two kiwis a day his constipation was gone. Obviously in the end the poor boy got fed up with kiwis and we were back to square one!
I think his constipation has also definitely improved since he has been potty trained, but I know of other children who started being constipated after potty training.
I agree with all of you who found GPs were not very helpful.In our case diet was not the problem, our son has always eaten lots of vegetables and fruit. In the end I was so fed up with well meaning people telling me to try some prune juice!