3 y/o with bowel problems *tmi pictures posted*

My son is 3 almost 4 and has bowel problems for probably a year now & he is currently on lactulose but I feel like something else needs done ... he doesn’t use the restroom every day, he uses it maybe every 2-4 days & when he goes & it so big that he cries when he pushes ... I feel so bad & I just don’t know what to do anymore. I’ve also upped his fiber but it’s not helping either & yes he drink water, I hardly give him juice but I have tired it to help him go & nothing ... I’ve posted pics below to show how big it is when he goes. Anyone else go/going through this????

EDIT **** he has seen a specialist & she is the one who put him on the lactulose. She also did blood work & X-ray.