Well, a doctor's visit is probably in order, but unfortunately my experience with a lot of dermatologists has been "Gee, I have no idea... try this Cortisone cream and check back in a week..." That's a an oversimplification, and it's not a dig on dermatologists, it's just that the skin is ridiculously hard to diagnose.
Based on the tiny amount you mentioned in your post, the thought of shingles crossed my mind. When you get chicken pox you are at risk later in life for a disease called shingles. The chicken pox virus, once it has run its course, sits in the dorsal horn of the spinal cord, in different places in different people. Shingles is sort of an itchy, burning, "ants crawling on skin" condition in which the "sleeping" virus decides to wake up. Because it sits in the dorsal horn, it affects specific dermatomes in your body. Dermatomes are specific areas of skin supplied by a spinal nerve. Some people get reddening of the skin with shingles and the area it affects is a perfect dermatome map! It's really cool (but not for the patient). Shingles tends to flare up and go away, so maybe you have a mild case that's just not going away.
Not a whole lot works for shingles, in my experience, except for GOOD quality antiviral herbals (Echinacea and St. John's Wort...SJW is actually a very good antiviral, in addition to a slight antidepressant) and chiropractic care. I have seen patients who have chronic shingles infections clear up within days of a proper chiropractic adjustment. Must have to do with the effect of the adjustment on the dorsal horn.
Anyway, you may not even have shingles, but it's worth a look. Good luck and keep us posted!
Chiropractic care is health care for the 21st century.