I have a bump on my lower back thats hurts like crazy?

Bump lower back: Could be a boil , an infected sebacous cyst or rarely a growth. Would have it checked out by doctor /urgent care , as they can enlarge. May improve with antibiotics either topical like bacitracin or oral.

Could be...: If it is a tender lump down at the end of your tailbone it could be a cyst that is getting infected. If it is a lump that is in the muscles of the lower back that is tender then it could be a muscle spasm.