Long hard lump next to bottom rib bone. not the same on other side. its stuck to the bone. what could it be?

No short answer: We need to know how long you have had this, i would guess it has been there for most of your life, since you didn't describe any pain in the past in that area. I would guess that at some time you have fractured that rib and it healed with a bump. It probably was as a young child. But if it has appeared recently and is growing you need to see the doctor.