Had a cold which i thought i had beat without any medication from dr. then it turned into an aweful sinus infection. was given z pack. then prescribed?

Sinusitis: This is a common scenario in which to develop a sinus infection. An initial viral URTI that appears to be resolving, but then a sinus infection sets in. A Z-pak can work, although Amoxicillin or amoxicillin-clavulinic acid are preferred if you are not allergic, and should be given for at least 7 days, more often for 10 as adequate antibiotic penetration into sinus cavities takes some time.

A viral: Infection was complicated by bacterial sinusitis.