Hmm...as someone who did her postdoc work in Immunology and Allergy, hives are considered a Major allergic reaction. Your doc needs to know ASAP. Other causes of hives are many, but an infection is most common, at least in kids (especially strep throat, vaginal yeast infection, sinus infection, some viral infections - esp. Hepatits) But, the proplem with hives is, if they signal an allergic reaction to the drug, the next time they might not be just hives.