Was the clindamycin given orally, as a pill? If so, then the swelling and itch might be an allergy to clindamycin, but the fact that it's persisted for over 10 days argues otherwise. It may therefore be that the symptoms are not truly allergic in nature, and that the clindamycin is coincidental and unrelated. This may seem odd, but really isn't, as nonspecific itches happen all the time. They hang around a while and go away on their own, though treatment can make the interlude more livable.
The doctor will no doubt want to rule out infection (perhaps as you suggest yourself secondary to scratching.) Other possible approaches to treatment might involve antihistamines and topical treatments. Whether allergic or not, your symptoms seem likely to be short-lived and controllable. The allergist should help.
Best.
Dr. Rockoff