You might need to get a full workup done.
I am one of the lucky people who gets "progressive contact allergies." Which means, the allergic reaction begins immediately (though maybe only a rash or something mild) when I make contact with whatever it is, and reaches the peak of hives and welts five days later, and then gradually subsides over the course of about a week. (Though itchy! I have to have heavy duty prescription allergy meds, and still sleep with socks on my hands so I don't scratch in my sleep!) I've never gotten a workup done, since it's only occasional, but because of the progressive nature of my allergies, I will never know what it is without complete testing. (Can YOU remember EVERYTHING you came into contact with five days ago?)
This sounds like it could be both to me - something you come into contact with fairly often, but is also progressive, which would account for the variations in intensity that you seem to be experiencing, if I'm reading this right. Is there a pattern? Maybe, starting on the downhill side of the reaction, but then getting re-exposed, just in time to hit the peak several days later, before the previous reaction has finished going away. All over suggests food or something you use all over - Lotion. Detergent. Spray tanner. Shampoo running down after you wash your hair.
Hope you feel better quick.