Hmm, are you able to stretch the back at all? I’m wondering if it’s a bruise, if you pulled a muscle or if it’s nerve damage. I’m sure it isn’t nerve damage
I think it's a bruise then. Possibly a fracture depending on how hard you fell, but I'm guessing it's not. Bruises take longer to heal as you get older. Just rest, get enough sleep and use a pillow if you can to ease the pressure. I wouldn't be able to tell you unless I could observe it in person.