What Causes Movement In Stomach While UPT Is Negative?w

I have only had a period once since Dec 2010 and that was in March 2011. I feel movement in my stomach like a baby moving but pregnancy tests are negative, could I be pregnant? I have had 5 children,2miscarriages and a tubal after youngest who is 2. what is going on? I am 39 yrs old, 5'3" and about 170lbs