After playing volleyball I feel pain at the bottom part of the neck on the back side where the spine starts. Pressing the spine bone is painful. Help.?

Overuse injury. Their are several muscles that attach to that area that are involved in extending the head and reaching back at the same time. The action of hitting a spike uses muscles attached to this area. Repetitive use that injures this area can result in a type of injury similar to "tennis elbow" or "shin splints". Ice and rest is very important to prevent significant injury. See doc if not improved!
Neck Spain. That bone is where your neck ends and you upper back begins. You have probably sprained the muscles connected to those bones. It is a common mistake because the bone protrudes so, to want to rub, rub, rub. From which you can make this more.