I had this a few years ago. My job was mostly warehouse based but changed to include quite a bit of office work too, so I changed my footwear from steel toe boots to steel toe oxfords. A few weeks later I got up in the night and when I walked it felt like I was standing on a nail. This continued to happen after a period of inactivity, stabbing pain under my foot near the heel.
I made an appointment to see a foot specialist (podiatrist?) and he diagnosed plantar fasciitis and asked if I had recently changed my footwear as this can be a cause of it. He also wanted to sell me some expensive inserts for my shoes! I declined his offer and threw away the oxfords and went back to wearing the wider fitting steel toe boots and have never suffered with it again.
If you have recently started to wear new footwear, that could be causing the problem, stop wearing them and buy some wider fitting footwear or go back to your previous footwear before buying inserts, it may not work but it may save you some money and discomfort