Sleeping on a strange mattress, especially one that’s well-used and fairly old, can definitely knock things out of whack. Last year I spent nine days in a seedy motel and my back was literally screaming by the end of the vacation. (A visit to the back doctor fixed everything, though.) Buying a brand new mattress is usually pretty safe, back-wise.
btw i used pillows in the ways mentioned and they helped some but the kicker was the wheat. It is super hard, esp if you eat out to avoid it, but if you can do so for a week or two the pain should disappear entirely (assuming you are dealing with the same issue)