The only thing I can think of is I just used a new detergent along with bleach. Would a reaction to your shirt cause hives all over your body?
I think it likely could, but hives are funny and can be totally flukey (I think). Where they were all over your body, I think I'd suspect something else, but since the detergent is new, it's probably the most sensible thing to investigate.
Allergies are also unpredictable. Once you're sensitized, you can react to stuff that wouldn't normally cause you to react. For example, normally, scented things don't bother me. But, if I'm already reacting to pollen in the air, even a candle scented with something that doesn't bother me (like cinnamon) will bother me.
I stopped eating stuff with MSG, for a variety of reasons. I knew it could sometimes trigger migraines in me (not the painful headachey ones; the ocular ones, which were followed by a headache, but a seemingly ordinary one). Then one day, I was cooking supper, and used canned gravy. I got some on my finger, and it itched like crazy, but I thought it was a coincidence. Then I ate supper, and got nauseated and headachy (all I could think of was Mrs. Cravitz from Bewitched, and her sick headaches). I took Benedryl on the off chance it might help, and I was better in minutes. I looked back at all the times I'd felt crappy when I ate chicken, and realized I served Rice-A-Roni (loaded with MSG) with it a lot, because the kids and Scott loved it. I stopped cooking Rice-A-Roni with chicken, and didn't feel crappy after I ate chicken.