Id like to try to help you but I need some more information. Exactly where on your lower back is this rash? How large an area does it cover and what shape is it? (Circular, etc). Have you used any new products prior to this rash or started any new medications recently? Does any of your close contacts- those you live with - also have a rash?
Have you ever had the chicken pox?
Thank you for clarifying,
It's about the size of a kiwi and is an oval shaped patch. It is around my belt line on the right side of my back about 2 inches from my spine. We changed laundry detergents recently but I went back to Tide. If it's from detergent wouldn't the benadryl cream and tablets have helped? Also, why only such a small area? Also in the winter especially I get really dry skin and I have been very itchy lately. I did buy Aveeno lotion for dry skin and it took the itchyness away. I have not put the Aveeno on my back. I use it on my legs, feet, arms & hands.
I had chicken pox when I was a kid and my children both had them about 10 years ago. We have all had a bit of a head cold go through the house in the last month but I am the only one with this rash. I probably wouldn't even be worrying about it except that when I accidentally scratch it, it hurts so bad I cry out. That is the only time it really is bothersome.
I have not started any new medications.
Thanks for supplying this additional detail. While online I cant state with certainty what anything is, I can surely give you my best guess based on what you wrote.
A possibility I am considering is that you may have ringworm. This is not caused by any worms; the fungus that causes ringworm got its name because it leaves round lesions. They are red, itchy, and can leave a crust, but not always. If this is ringworm, simple cases are treatable by over the counter anti fungal ointments- the type you'd use on athletes foot. Clotrimazole, for instance. Fungal rashes take a while to go away with treatment, a few weeks. As ringworm is a fungus, the benadryl and polysporin wont really help. I am happy you didn't try hydrocortisone cream, as if its a fungal rash, rashes on steroids tend to grow.
Another (and to my mind) less likely possibility is that this is the rash of shingles. Shingles is a reactivated form of the chicken pox, and as the virus lives along nerve cells, it will create a rash along the path of a nerve...on one side of the body. The pain here though is usually intense; I mention it because you describe it as "burning" when you scratch it, and nerve pain can be that.
I suggest a visit to your doctor to find out what this rash is; both ringworm and shingles are contagious. And, I cant online tell you which it is; only an in person doctors exam can appropriately diagnose and treat.
Here is more information on ringworm: The pictures on the right side of the article show severe cases; your rash (if ringworm) is not so severe and may look somewhat different. http://www.nlm.nih.gov/medlineplus/ency/article/001439.htm
I hope I was able to help,
You are so welcome...and I hope you feel better. Ringworm isn't too pleasant...but again I have to caution you not to diagnose anything over the internet; in person evaluation is the only way to get diagnosis. But I'm happy to provide information :)