Knocked my thumb on metal stair rail 2 weeks ago, hurt at the time, now lump about 1cm at site of injury, I have low vitd and osteopinea. Fracture?

Not sure but. A lump with pain after trauma to a bone can be...So it sounds like you need an exam and maybe an xray if the exam confirms your own suspicions.
Get xray. Sounds like a contusion w/ a small hematoma that's formed ' knot' there. To be sure though, see an ors and get an x-ray! Good luck!