Perhaps you broke a blood vessel. I've never heard of a blood clot so close to the surface of the skin, but I'm not a doctor either. If it doesn't get better in a few days, you might have it looked at by a doctor.
I'd tend to agree with Mocha that it's a hematoma. Are you on any blood thinners?
You'd expect a clot more from immobility than from exertion.
The one thing that argues against a hematoma is that you don't mention discoloration.
Thanks for the imput. I've been putting cold compresses intermit tingly on it, I will have it looked at if doesn't get better.