What Could The Small Weird Beating Inside The Stomach Be?

i have been having wierd beeting and small movement on my left side of my stomach. its only by my belly botton and its hard just in that area.On my right side there is no beating or movement and is soft unlike the other. I have the marina but my periods were heavy and two months ago stopped conpleatly. i already have one child. I have also been having pain around my cervix where my iud is. i have taken two PT's and they both show negitive. what is your opinon on what it could be