Suggest Remedy For Stool Withholding

Hi I am a mother of a 4.5 year old boy. My son has a problem with stool witholding for about four months now. He solis his pants with some stool from the 3 rd day from the last bm. He goes about every 8 days, or sometimes 6 or 7. He sits on the potty couple times a day it seems he will produce a stool, it smells, but the he witholds and the stool doesn t come out. I think he is afraid that it will hard him when he goes. He got constipated around august, hte stool was after 8 days, very hard and some blood on it. He had an infection of the throat then and didn t want to eat anything, so I gave him some chocolate desert he likes and some other things that made him constipated, because I was afraid he didn t want to eat and loose wait, not be able to fitght the infection. Since then he has been witholding the stool. I went to the peditrician, she said to take decoman and that didn t work so we tried lactulose, after that was no improvement in frequency and he had cramps and his behavior was different. He was irritated a lot. I look him of lactulose and I don t know what to do next. He had an ultrasound, but it didn t show anything specific. The doctor who preformed the ultrasound said that there is some fecal matter in the stool. Now doctor is saying he needs an x-ray with contrast or somethin. I would be thankfull for any advice. I don t know how to help my son, so he can go more often and the stools are not as hard. I give him prunes, otmeal, fresh apples and pears.. he doesn t eat nay chocolate or bannanas-nothing that will make him constipated more. Thank You for any advice.