Ouch! I can relate to being itchy!
I have a skin condition called "Dermatographism". Hives are readily produced if the skin is lightly scratched. It's also called "Travelling Hives", because the more you scratch the more you itch.
You can see pictures of the results at the following links:http://www.nlm.nih.gov/medlineplus/e...pages/2780.htmhttp://www.nlm.nih.gov/medlineplus/e...cle/000005.htm
I cannot use my finger nails to scratch an itch because it just makes it worse. When I have an itch and need to scratch, I have to use something hard and rough, like a bristle brush or a dry loofah, otherwise I get welts that itch more
My favourite back scratching tool is actually the serated blade of an electric knife.
I practically live on Benadryl and always have to have some in my purse and at home because I would go mad if I didn't have any when I needed it. When my back is itchy, the itch is so intense that I practically rip my clothing off my body so that I can get at it to scratch.
Are you on any new medication? Tried a new cologne or deodorant or shampoo etc? It's possible that you may have come in contact with something that someone else was wearing. Perhaps brushed up against them and they were using a product that you are allergic too.
Of course it could be stress as you mentioned. The body has all kinds of ways of reacting when under stress, and hives is one of them.
Benadryl should have worked. Did you take 1 or 2 pills? Two pills is the usual dose. Also it's important to get the right type. You want "Benadryl Allergy", not Benadryl Cold and Sinus. The allergy one counters the histamine effect that is the cause of itchiness.