I have on my back my skin is kind of hard in an arear its in extreme pain and what is it?

See derm. You definitely need to see a dermatologist to diagnose this. There are different reasons the skin can become indurated or hard, including but not limited to infection, connective tissue disorders, trauma.
Infection. Usually painful lump could be infection, abcess or cellulitis. Have this taken a look if it is sudden.