Oregano oil is a very potent extract. I'm not at all surprised it clears things up.
I got a chronic sinus infection from swim training at the local pools. Antibiotics never really helped and I carried that infection for a few years before I finally tired treating it myself with Australian tea tree oil steam inhalations.
Just 15 mins every night, no rinses or anything else. Within 2 weeks it was gone, and it's never been back. These two essential oils are dynamite on infections.