My finger got slammed in the trunk, weeks later, there's an odd lump in the bone and it hurts really bad! do i need to see a doctor?

May be a little late: At this point, there's not much a physician can do that you can't do yourself. You may have incurred a chip fracture of your finger. Immobilize it with a finger splint that you can buy in a drug store. Keep it immobilized for at least three weeks, and hope that the fracture will heal (it takes about six weeks for most fractures).