Sorry to hear that you hit your head! It is pretty common when this happens for a bruise
or at least swelling of the soft tissue of the scalp to form. This tissue is pretty tender and is susceptible to injury. Generally, however, this is not a big deal and it will go away on its own, although it may take several days for the tenderness and swelling to go down.
To help things along, you may want to try icing the area; this will limit the swelling. Similarly an over the counter anti inflammatory medication like ibuprofen or naprosyn should help with the swelling and should also cut down on the pain somewhat.
There is no need to see a doctor
for an injury like this unless the area that is involved is very large or if there is severe pain. Also, if things are not starting to get better in a day or two, you should see your primary care doctor
. Finally, if you have any signs that the hit to your head may have caused more damage than just a bump - symptoms like headache, nausea, light sensitivity, or dizziness-- then you should see your doctor immediately, as these may be signs of a concussion.