can anyone help please? my little boy has bad constipation he was ill not.long ago but wouldn't…

can anyone help please?

my little boy has bad constipation he was ill not.long ago but wouldn't drink nothing but his milk which he only has twice a day. I tried water, juice, fresh juice smoothies, ice lollies anything you could possibly think of, I even tried in different cups and bottles so due to that he's got constipated and it's built up, he's now drinking loads again but really constipated, he's in agony when he poos he even crosses his legs over it hurts him so much, I've been to the doctors with him, he's had lactose which didn't work and he's now on movicol which he started yesterday, is there anything else that will help him go he's in agony? he's having plenty of fruit and veg and fibre to help him, he's 13 months old? hate seeing him in pain 😢💔