Hi, I have been cashiering for 10 years. Until this year, I haven t had any problems. I walk regularly and try to do stretch exercises and use special good feet pads inside shoes. However, now I ve been having severe problems with the right knee. It feels like the muscles turn into solid rock half way through my shift. I sleep with legs over two pillows, have done that for years. Now today, I was home from work and was going up and down the stairs and cleaning and the back of knee twinged with pain as well as the rock feeling and it is hindering me as to what to do, since we planned to go on vacation tommorrow and I notice the pain is the worst when I drive. What could it be and how can I heal it?