Guaifenesin and hives

I was taking an over the counter guaifenesin-based cough syrup twice a day (150mg each dose) for approximately 10 days in an attempt to make my cough more productive. A nickel-sized pink patch appeared on the right side of my chin. I continued to take the guaifenesin thinking the reaction on my face was contact dermatitis from my phone. The pink patch turned dark red, then got very swollen (the whole lower side of my face swelled) and began to weep clear fluid. I immediately stopped taking the guai (I hadn't used my phone for days, clearly it was not the culprit). Surrounding the original red patch was a new pink patch which looked like it was going to take the same route, but because I stopped taking the guaifenesin the reaction was never as severe. The hives eventually scaled over and peeled.