Yes, do what Charlee says!!! If you've had hives before, then there are certain "on-going" things you are allergic to. Although you tend toward allergies, something can pop up one day that you've never come in contact with before. I'm very allergic to mold and will stop breathing. If the store where the muffins were had mold on anything NEAR the muffins it could affect you. My allergist told me that once you have the hives, they will reappear over and over...not like your body builds up immunity to them. If you don't get relief soon, I'd go get a Benedryl shot. There's another one that works well but can't remember the name.
Feel better soon...know you are miserable!!