Since it always comes back in roughly the same spot and produces blisters, I assume this is herpes. The location suggests that it is genital herpes. The way to diagnose it is to culture a blister when it's fresh, although a type-specific herpes 2 blood test can be done at any time, and is quite reliable.
I suggest you get these tests done as soon as practical. If it turns out to be herpes, then depending on whether you have a regular sexual partner and other personal details you can learn about the best way to deal with the problem and what precautions to take.
Best.
Dr. Rockoff
To my knowledge, HSV outbreaks occuring only on the leg and far from the genital region (on penis shaft or vaginal region) is rare but can happen. Depending how long after your initial symptoms (DEC 05) you had your testing done depends on the accuracy of your result(most tests are 95%+ accurate (I believe somewhere between 6-14 weeks). Type specific tests are necessary due to their ability to distinguish between HSV 1 and 2. Type specific are more accurate as well. You can get free testing at local free clinics. Call your local health department for testing locations.
IgG TESTING INFO
http://www.racoon.com/herpes/healthcheckusa_testing.htm
HERPESELECT INFO
http://www.questdiagnostics.com/hcp/topics/herpeselect/herpeselect.html