Hi there,
If you think that something is terribly wrong with your nipple,please don't.You simply bumped your nipple too hard on the floor resulting in injury to delicate blood vessels causing bleeding under the skin,pain and maybe a little lump under the nipple.This would happen on any other part of your body if it were injured.
Apply cold compresses and see how it goes.Your mom is wise to take you to a doctor for an exam so you can be assured that there is nothing serious there.Okay?
Take care ..