Have noticed in past 10 years or so that w/in few days of finishing a course of antibiotics, i tend to develop a rash on neck and upper chest. has happened 2x w/doxycycline & now w/clindamycin, tho not as severe as doxy rash. is this an allergy?

Probably not: Probably a coincidence. It is rare, if ever, that an allergic drug rash would start after the drug is stopped, especially "a few days" later. With both clindamycin and doxycycline, the drug is gone from the system within a few days of the last dose. Discuss with your doctor, and grease the skids for an immediate visit if it happens again, so she can examine the rash. In meantime, I wouldn't worry.