How long has this been going on and when did you give him medication? Is this your 10 year old?
Pepto Bismol is not recommended for children under age 12 due to the risk of Reye Syndrome (which is the same reason you don't give Aspirin to children). The maximum adult dose is 8 tablets a day so for a child, even if a doctor recommends it, it sounds like 6 is too high a dose in a day. Not only that, it's not a good idea to try to stop acute diarrhea - it's the body's way of getting rid of whatever is bothering the digestive tract.
Given that you've given your child a lot of a medication that's not recommended for children and he's in a lot of pain, I would at the very least call your doctor. The diarrhea makes it sound like it's viral and not something like his appendix but most kids don't cry and scream over a stomach virus.
If the doctor thinks it's just a virus, it should pass soon. Don't give him any more medication, the diarrhea is the body's most effective way of ridding his intestinal tract of whatever is bothering him. Keep him hydrated and try the BRAT (bananas, rice, applesauce & toast) diet.
Really...this is not normal so please call his doctor.