It could be that you have bruised your coccyx
or tailbone and this can be quite painful and the bruising could cause a lump to be felt. If this is the case it will eventually disappear and you do not need to do anything.
There is a possibility that you have a cyst
at the base of your tailbone. This is not serious but it may become inflamed or infected. If this happens you would notice persisting pain and possibly discharge. In which case you should see your doctor as antibiotics may be needed.
Hope this helps you.
Dr K A Pottinger,