How Can Chronic Constipation In A Child Be Treated?

My 7 year old grandson use to suffer from chronic constipation, from the time he was 2-1/2 until 5-1/2. We have had him to a pediatrician that specialized in this. Eventually he grew out of it or so we thought. About a week ago it started just like square one. Co stipation, painful urination. Screaming with stomach spasms and saying his penis was sore so not urinating as he should. We put him back on Lansoyl and it helped a bit, he has 2 bowel movements during the night. He is in my care now while his parents are away. His last bowel movement was Thursday night. I have had to keep him home from school on Friday. He sleep walks and screams so we lead him to the toilet where sometimes he will have his bowel movement but the high fibre, fruit and lansoyl is not working this time. I do t know if it is psychological or a medical issue. We have fought this battle for so long and just when we thought he was over it we are back to square one. Do you have any recommendations? Please! This is such a sad situation, he hasn t gone out to even play in 4-5 days. Any help would be greatly appreciated. Thank you for listening. Dolores