What's the best way to deal with foot pain when working retail?

I just started a new job where I stand all day (9 and a half hours, minus a half hour lunch break.) About two hours into each day, my feet start getting sore, especially my heels. I’ve bought a new pair of sneakers and tried a couple different pairs of inserts, but nothing has helped so far.

Sitting down brings some temporary relief, but my feet usually start hurting again after a half an hour or so. Pain killers take the edge off a bit, but they’re not really effective and I don’t want to take them every day. Mostly it’s a sharp, persistent pain in my heels whenever I’m standing.

This seems to be a new problem. I’ve had no problem standing for long periods in past jobs. If you’ve dealt with something similar, what was the cause and how did you fix it? Thanks.