I have a small lump on the top of my head.i came up from a cubby whole and didn't back down far enough.it hurts when i lightly touch itshouldi seeadoc?

How long???: Headache? Visual symptoms? Headache? Bleeding? Nausea? If in doubt, check it out.

Depends: If you have any other symptoms such as vision changes or nausea/vomiting, you should see a doctor immediately. If you only have tenderness at the site of impact, try placing an ice pack on the site.

Yes: It would be best to have it examined, measured, and see if it needs imaging or not. That's best done on a physical exam, and your primary care doctor can do it. It could be anything, and probably benign, but you want to get professional care and opinion in case it's more involved than you think. Good luck!