Eating Habits/ Encopresis

Hi, my son will be eight years old in September. He was diagnosed in July 2007 with encopresis, and has been taking the laxative Miralax ever since. In May 2008, he started having problems with frequent urination, going every one to two minutes. He is still being seen in the GI clinic, and by a Urologist for these conditions. As far as the urination problem, no one seems to be able to figure out why he is urinating so frequently. He doesn't wet the bed at night, and never gets up in the middle of the night. It's only durning the daytime. His doctor has tested him for diabetes, and infections, and they all have come back negative.

At one time, I thought it could be anxiety, but during the day when he is relaxed (watching T.V., or playing with his cars) he is still running back and forth to the bathroom. His urologist mentioned a medication that he could take for this problem, but one of the side effects is constipation and he already has problems with constipation. My son was finally fully potty trained when he was five years old, and I feel like with all of these other conditions, that he's going backwards instead of forwards.

I've heard that some children with SPD have encopresis because of their eating habits, but I'm not understanding the frequent urination. (Also, I forget to mention that at one time the doctors thought that the constipation could be pressing on his bladder and causing him to have to urinate so often, but even at times when his x-rayed showed that he had cleaned out, he was still urinating frequently). Has anyone ever experienced a child with frequent urination and had a diagnosis as to what it was? Thank You.