What Could Cause Recurring Stomach Pain Followed By Watery Stool In My Toddler?

My kid is of 3 years old...He mostly have stomach pain...and after that watery potty....He use to suck his thumb...I hav shown the pediatrician he has given cyclopam and oflomac forte...In the period of 2 to 3 months he have this problem....can u suggest some advice...