B1
pain in your back
Dictionary examples:
I got a backache from nodding too much during my boss's boring speech. (0.0)
My wallet causes backache. It's too full of money... just kidding! (0.0)
After trying to lift his cat, Tom got a backache. His cat weighs 200 pounds! (0.0)
I had terrible backache last week. (19.3)