<human>: Can you summarize the given text in a few sentences?

Hello everyone. 
Usually I can maintain a 7:34 mile average on a run spanning over 4.5 miles. However, recently I have been working in a retail store and I am constantly on my feet and moving around; I mention this because since I started there my running is horrible. I can't even complete a 3 mile run without having intense pain in my lower calves and shins. 

I feel like the two are related, but I don't know exactly. Do any of you have any advice, I'm really at a loss and just unhappy with how my performances have been these last two runs.

Thank you for you time.
<bot>: Working at a retail store, always on my feet. Can't even complete a 3 mile run and have massive lower calve and shin pain; is it related and what can I do?