Do I have a concussion? Didn't pass out or get confused but head STILL hurts.?

The other day I had a go kart accident -- I must've been going full speed, though I'm not sure what that speed was, and there was a hairpin turn. I hit the person in front of me harder than I think I've ever hit anything (including a real car accident I had once that bent up the front of my car) -- and my head whipped forward. Actually, my entire body would have left the seat if there wasn't a seat belt that covered my whole torso-- but nothing held my head in place, so forward it went.

My head did not have impact with anything, but my GOSH it was like hitting a wall, and I had a headache for the entire day following. The back of my head and the area behind my forehead hurt, while my neck was oddly okay (at least til the next day, when my neck started to hurt too.)

I wasn't too dizzy afterward (finished the race anyway. Wasn't able to assess until 10 mins later). The sunlight was unpleasant, and made my head hurt more. But I wasn't nauseous. Nor was I confused.

Today, two days later, I still am having frequent headaches, though. I thought it was heat exhaustion but it's in the same area as it was the other day. The area right behind the middle of my forehead. Neck still hurts too, but I'm trying not to be a baby about it. I've been wanting to get a massage for a neckache for ages anyway; I imagine the impact just made that worse.

Is it possible I had a mild concussion, without being dizzy/nauseous? What do I do to fix it?