Am I harming myself performing my job as a cashier?

I stand in one place for about three and a half hours at a time with minimal movement. I lift bags that weigh easily ten to fifteen pounds easily 100–150 times a day. I speak to people for extended periods of time. I open grocery bags that leave my hands dry, and chapped.

Here are a few ounces of prevention that seem to minimalize the wearing down of my body, but will standing or moving so much lead to nerve damage or anything else bad?

I stand on a very cushy mat, I use lotion on my hands, I stretch and walk at least a few paces inside my register area between customers, I take very expensive vitamins to replace any nutrients that I might be losing, I drink lots of water (>1l/day) .

Maybe I am wrong for being concerned, and the work might be a form of exercise?

What do you recommend?