I was playing volleyball, dove for a ball then slammed the back of my head on the ground. I got a headache right after it happened and I began to feel sick and shaky during the game.
Are these signs of a concussion or am I just thinking too much into it

I'm not a doctor, so this isn't a medical opinion, but I'm a horseman and have had three concussions and a bunch of non-concussion head injuries. It comes with the sport. LOL The symptoms you're describing have been common to all of my head injuries. The difference with the concussions was that I was actually knocked out and since I didn't seek treatment for all of them, in one case I actually became temporarily paralyzed during the night. That's a scary experience. If this just happened, you really should get a doctor to look at you. My nephew suffered a skull fracture which required medical treatment and he had a less-offensive accident than any of mine. It all depends on the angle of the impact.