Kid with very large stool

[Paul_B1]

Good day.
I am concerned about this peculiar situation refering to my son. He is 12 years old. Weight :46 kg  (101 pounds)    Height:  4 feet 11 inches (1.49 m) His habits of going to the bathroom are such that defecates from once a day to once every 3 days. He has been like for more than 6 years.
But the problem is that very often when he defecates his stool is huge, from my point of view. I mean really thick. I am 42 years old and his stool has a diameter 6 times wider than mine. And I think 5 years ago, when he was very young, the size was the same. We are used to him clogging every toilet in the house. He sometimes has stomach ache, but he is used to it.
The lenght of the stool is about 12 cm. not to large relatively, it looks like a rock.  
I have tried to include one fruit daily in his diet, and whole wheat bread, some yogurt.

Please advise. I need to know if this is something that must be treated.
Thank you for your comments.

[Caryopteris]

I would caution you not to blame your son.  I have seen where doctors have claimed that kids sometimes ignored the urge to go to the bathroom.  I don't know about that.  It certainly was not the case for me, although the fact we had 6 people using 2 bathrooms could have contributed to things when I was very little.  But I also remember when I worked with nurses, they would describe the difference in their infants.  The one who had good bowel function were happy babies, and those who struggled were cranky.  Although they were smart enough to observe this, they still didn't have the wisdom to see they needed to change something to help the cranky child move their bowels.  Certainly you can't blame an infant for how their bowels move, but a parent who is really paying attention would notice two children who were different.  My mother should have noticed because the problem I have is just like her, and she almost died in her 40s from a ruptured diverticulum.  She had been going to doctors for 6 months, complaining of abdominal pain, and they only checked her for "female trouble."  When all that came back normal, they said it was all in her head.  Her abscess and peritonitis and need for emergency bowel surgery suggest otherwise.  It turned out she had a long, twisted bowel, so that's why I think that's what I have.  

So when you suggest it could be behavioral, I caution you that it may have nothing to do with behavior and habits, like lazy doctors like to pretend.  

[Paul_B1]

Thank you for your comment.
It has been very helpful. I am going to contact a gastroenterologist. I already tried this years ago, with a doctor with very good reputation, who told me that we are all different and that there is no problem.
Your comment makes me realize maybe even certain behavior issues may be a side effects of this situation.
I understand how with everyday activities this is easily overlooked.
By using your experience to help others like me, you are being a blessing.
I hope you are able to find help with your health problems.