When I bend over, the lower part of spine sticks out. Not the spine but there are two "muscles" along the spine that pop out? What is going on?

Varies. There are a number of possibilities, I would not hesitate to be seen. Could represent normal paraspinal muscles or related to a variety of spinal deformities among other possible causes. A detailed exam would likely show the cause followed by appropriate radiologic studies.
Normal curvature. The normal curvature of the spine allows the lower part to stick out when you bend. That is the lumbar spine. The thoracic spine do not since the have ribs attached. Your doctor evaluates you as you are growing to evaluate you for sciolosis. If you are concerned see him/her.