Please advise if it's normal to have a lump on the lower spine?

Depends: This would depend on the nature of the lump. I assume that you are referring to a lump that you can see on the back. If it is new and growing and painful-it needs to be checked out to make certain that it is not a tumor or infection. It is is boggy or has fluid, it needs to be checked out as it might represent a connection down into the spinal canal.