I realize you asked this question over a year ago, but just so you know I also have that same problem...usually during the summer when I wear shorts. It seems like my lower legs get these sores as soon as I wear shorts and finally heal up when fall comes and I'm sporting pants.  I asked my doc about it and was told I might have an allergy....I'm assuming an allergy that just affects my lower legs and it's a reaction to open air...   I was hoping you had another answer already, but I'm just letting you know that I have been dealing with this problem ever since I had my first child 13 years ago.