How long does it take for a sinus infection to go away?

Three weeks: Three weeks. Takes three months for sinus to get back to "Normal" provided not chronic or recurrent in nature. Also depends on allergies, irritants, mucosal disease, etc

Depends on cause: Most, if viral, resolve in 10-14 days. Fungal or chronic bacterial sinus infections may require treatment and would persist longer without it. If a recurrent problem, then the immune system can be evaluated. Also would need to treat any chronic allergic or non-allergic rhinitis (chronic congestion, loss of smell, nasal drip, sneezing/itching etc).

2-3 weeks: With or without antibiotics.

Sinus infections: Sinusitis sometimes becomes chronic and may nit go away without treatment. See an ENT specialist for a definitive diagnosis and treatment.