A few years back, I got stung on my face during a ride. The initial allergic reaction was pretty minimal, but a day or two later, the area grew red, swollen, warm to the touch and itchy. It turned out that it had gotten infected. According to the nurse practitioner I saw about it, it's pretty common for a sting to get infected. A short round of antibiotics cleared it right up. I'm no doctor, but I wonder if that's what you're experiencing.