What Causes Abdominal Pain During Passing Of Stools?

Hi My son is 10 and every morning when he goes to the toilet for his regular bowl movement, he has painful cramps in his abdomin. This can last 5-10 min, even after his bowl movement which is not too hard or soft. At time he can break out in a sweat from the pain. I give him a heat pack and we just wait until it passes. This is not normal and I already have the heat pack warming when he goes to the bathroom.