Try to go back to work, take it one day at a time, the most important thing to slowly learn is that you can actually be ok around people, often it is better with people you don't know because they are not expecting you to be anything more then what you are doing behind that counter as a cashier. You also may find that you slowly develop a resistance to the noise in the place where you work too. Sometimes consistent noise is better than having it quiet and then sudden noises. I found that I sleep better with the TV on for example, because it is constant noise and I think that has been better then too much quiet.