Did you eat or touch anything that could have caused this reaction?
Sometimes bacterial infections can cause itchiness with feelings of hot and shivery.
Have cool showers to help cool down the skin. Don't use any soaps or shower gels.
I suggest you see your doctor.
By natural antihistamines, do you mean benedryl, or some sort of supplement? Benedryl is the way to go as a first line, even if it makes you sleepy. At the very least take it at night. You can also get some 1% hydrocortisone over the counter, which should help with the itch and puffiness. If it doesn't get better in the next few days, you should see a doctor. If you start having trouble breathing or get a fever, you should go to the ER.