Why am I itching???????

[ny biker]

This just started a little while ago. I was sitting on the couch, watching TV. Wearing a cotton short-sleeved shirt with a scoop neck. My neck started to itch, so I scratched. Itched more, scratched more. Etc. Next thing I know, it starts to itch in front of and below my armpits and on my back, under the edges of my bra.

So I took off the shirt and bra and of course started scratching all over (stupid, I know). Then I took a piece of wet paper towel and sponged off the whole area, which helped a bit. Now I'm in my cotton pjs, trying hard to not scratch and make it worse again.

The skin all around the base of my neck is all red, as is the skin where it was itching under the bra. There are no hives, welts, rash, or anything like that.

I just took a Claritin.

What could cause this kind of allergic reaction? The shirt is several years old, the bra is a couple of months old. I use 7th Generation laundry detergent, but that wouldn't be the problem since my other clothes didn't cause itching in other areas.

Could this be a reaction to something internal, like a food I've eaten recently? Or is it more likely contact dermatitis?

I've had mystery allergic skin issues before (hive-like welts on various parts of my body) as well as rashes whose origins I never identified. Plus of course the identifiable issues like poison ivy and certain brands of deodorant.

I did put lotion on this morning on this areas, but it was two different kinds: Eucerin face lotion with non-chemical sunblock on my chest and neck and Complex 15 lotion around my armpits where I sometimes have dry skin/chafing issues.

Ugh I want the Claritin to kick in now!!!!!

update: red skin is spreading from neck down to the tops of my shoulders and up my back.