First... remove the bedding from his cage and keep him on paper towels. You need to minimize rubbing on that lump and you need to keep things as clean as possible.
Second... What is that silver-colored sliver near the bottom of the lump? If your snake has something stuck in him, carefully pull it back out along the impalement trajectory. Use a tissue to very gently apply pressure around (around, not on top) of the swollen mass to help it drain. Keep the snake on the antibiotics.
You will most likely need someone to hold your snake while you do this.
please keep this thread updated. Good luck.