What Causes Hives All Over Torso After Taking Clindamycin?

I started taking Clindomycin this morning, and this afternoon I developed hives all over my torso.I am allergic to penicillin and morphine (broke out in a bad rash from those, but no hives), but took Clindomycin a couple months ago with no problems. Could this antibiotic cause hives (they are like welts). no other symptoms and didn t do or eat anything different today besides get novocain at the dentist this morning