only child

For 3 years my son has had bowel movements that are small round pellets, he is 6 years old. He does have a bm everyday. I think we eat a good diet, he drinks water and juices each day. He eats fruit, and vegetables. His doctor says not to worry, but I do. For about 2 months we have been giving him a yummi fiber (chewable) 2 a day. What else can I do?