Yes, you can use things like saline nasal sprays, or neti pots (they are sold with instructions). None of this will do any harm if you have a real infection; they just won't work. However, absolutely avoid spray decongestants such as Afrin and generic versions. They end up doing more harm than good, especially if used for more than a couple of days.
Keep in mind sinusitis is actually not all that common. It happens, but it's frequently confused with severe sinus congestion, which is not an infection but can be almost as uncomfortable. Only a thorough examination by a medical professional will tell the difference and the treatment is different. Simple congestion does not resolve with antibiotics, and antibiotics alone are sometimes not enough for complicated sinusitides.
My suggestion to you is try something like the above. If you don't get relief in a few days or it gets considerably worse, have it checked out.
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