9 month old, always constipated!

[LONC2012]

My 9 month old DS has suffered from constipation from around 7 months. He was prescribed Laxido which started to help after a few days and after about a good week he started going much better, he was also on antibiotics so I'm not sure if this has been the cause of the better poo's, so I stopped the Laxido as the GP had said once he starts to go better then to stop the Laxido. However he is now going back to square one, crying in pain every time he poo's and it's like a hard stone in his nappy. I have started back on the Laxido but I'm now worrying that there is something underlying causing this and wondering if there's anything better than Laxido to give him as k struggle to get him to drink it all?

Thanks