Mysterious lump on bottom of spine?

[Laura]

hi ya, writing this on behalf on my boyfriend he has a strange lump on the bottom of his spine. He was doing martial arts at the time and landed flat on his back which then the lump appeared. its been there a week now. it hasnt gone down or moved or nothing. its tender to lean on but as hard as bone. it looks as though its on the spine as its in the exactly line of the spine. could this be swelling or something? but wouldnt it have gone down after a week? has anyone had this before?

thanks in advance.