I m a 33 year old female in good health. But on occasion, I get some sort of pimple/sore in my hairline on the back of my neck. At first all I will feel the bump. If I scratch it, it kind of blisters up and gets larger. It is very tender and red all around it. There is only a clear fluid in it. I have a hard time not picking at it. This has happened before but not often. I always assumed it was a pimple. It is circular. The middle of it is where it looks more like a blister and around it the skin gets hard and then it is red outside of that. Usually after a couple weeks, it just goes away on it s own. I have had chicken pox and thought maybe shingles???