I hit my head three weeks ago and it gave me a concussion. i still have a lump on my head three weeks later. should i be worried?

If you hit your head, and did not experience loss of consciousness, amnesia, or both, you did not have a concussion, and lump on head likely represents a local scalp hematoma ("goose egg").

A concussion is about what happens INSIDE your skull. That lump is OUTSIDE your skull. It has nothing to do with any "concussion." It's just a lump. If you're worried about the LUMP, see your doctor. If you're worried about the CONCUSSION, you should still see your doctor, but it's a separate question.