This is Dr. David
this sounds like a blister
or it could be due to a sebaceous cyst.
would you like to upload a photo of the spot?
do you have a doctor you can see who can look at it as well?
its none of them
can you upload a photo of the spot on the foot so I can better see what it looks like?
here are instructions to upload a digital clear jpg photo
type a word in the textbox and highlight itthen select the paper clip icon to upload a jpgthis opens a window where you can click next to the text box to select the jpg or pdf file on your computer to upload into JustAnswer