How do I know if the baby's belly is dropping or not?

How do I know if the baby's belly is dropping or not?? In recent days, the little one has been acting really strange, unlike usual. The heartburn seems to have passed, and there's no pressure on the bladder. But it moves a lot, but not such direct movements. They are frequent, but not really strongly felt. And before, it would spin all over the place, left and right. I don't know what this means.