 [ Symptoms ] 7 weeks ago i got a sinus infection zithromax helped thin the mucus but the congestion has lingered what can i do [ Disease ] from my own clinical experience i do not find zithromax strong enough for sinusitis sinusitis can be very difficult to treat and relapses are common i once had to remain on antibiotics for three months for my own infection you need to call your medical provider again i suspect you are going to need another course of a different antibiotic even though your mucous is clear