I fell and hurt my back last night. a spinal x ray showed no bony injury but have a large haematoma in the lumbar region. now vomiting. why?

Get to an ER: If you're not on new medicines, be safe not sorry: as you've had bleeding / bruising in the lumbar region, you can also have blood in the CSF, spinal canal, or brain. Blood in that space is a very powerful inducer of nausea & vomiting - a warning sign that something is wrong. Get a CT scan of the head (no contrast) to confirm. Go sooner, rather than later - bleeding in the brain can be fatal.