Sinus infections last from 1 to 2 weeks and can go away on their own without treatment.
However getting treatment and medicine for the sinus infection can help it go away possibly sooner and make you feel much better.
If your sinus infection is the acute sinus infection type then it should easily go away within a couple weeks but if you have a more severe chronic sinus infection then you might need more medical treatment and it could take a month or two for the sinus infection to go away.
When you have a sinus infection it would be best to see a doctor to get some prescription medicine to help treat the sinus infection.
You should also rinse your nasal passages out and stay hydrated with plenty of water.
Using a humidifier in your home or bedroom can also help with your sinus infection and try elevating your head and get plenty of rest.
When you do that then within a couple weeks the sinus infection should go away and if not then you have a more severe sinus infection that may require more treatment and can take a few months to even 3 months to fully go away.