if you are in the UK Op, then you probably have a small 'foreign body' in your foot and there is a little pus formed. Wash the area, puncture with a sterilised needle, let the pus out and cover with a plaster (blister plaster if you have one) and ot should heal up in a few days. However, ifyou live somewhere hot and exotic, with strange flies and boring insects, this could the beginning of a very interesting thread........ PS: I think you are supposed to start this type of topic by sounding the <<KLAXON>>
Athletes foot? I had that once with lots of little blisters on sole of one foot, though they leaked clear fluid when they burst and were itchy as well as sore. Might be worth trying an anti fungal treatment.