I would say that it is your top thread. it doesn't look like it has tension so it is either it is turned down to low or the thread didn't make the tension disks, like stated above, try rethreading it all, top and bottom, Check to see what the dial on the top says, and turn it up a little, it should be around the center of the numbers, you will be able to tell what thread is doing what if you use different colors on the top and bottom,