Are your shoes rubbing there?
Is it from a chemicel (SP)?
How did the blister form, or what did you do differently that may have caused it?
Have you covered it with mole skin to protect it from being irratated?
Have you been tested for Diabetes?
Soak your foot in hot water and allow the skin of the blister to soften. Scrub around the blister to remove all the dead skin you can. It should rub off easily. If the skin comes off the blister that is OK too. Cover the blister and surounding skin with a triple antibiotic like neosporin. Allow this to soak into the skin for about two hours. Before putting on your shoes cover the blister with the mole skin. This should clear up the blister in no time! If the blister continues to reappear See the doctor!!!