I had sinus allergy intermittently for about 50 years that gave me terrible headaches, 'stupid' brain (not thinking as well as normally), and tiredness. I never did have a sinus infection though, just allergy to pollen, dust, perfumes, cleaning products, etc. Antihistamines would lessen the swelling and congestion but did not help my thinking at all.
I have solved this problem for the past 15 years by following the blood-type diet Eat Right 4 Your Type. For the first three weeks I just eliminated the six foods said to be the worst for my type, and I knew I had a solution to my problem (my brain was working).
Other allergies I had are lessened. My energy level is superb for my age. I no longer have muscle stiffness, and I am much healthier than I was 20 years ago.
This is a FREE strategy. They say you can watch on an electromicroscope as the red blood cells pick up foods to distribute around the body, and some foods are not picked up by some people. Info is on the Net.
Best of luck.
You can try Colloidal Silver nasal spray. You can get it in a health food store or online. If that doesn't work, you may need antibiotics. That means a trip to the doctor, but if you're that miserable, it's worth it.
What symptoms do you have? How old are you? Do you have a history of allergy to any specific substances?
You should try steam inhalation, saline nasal drops and oral antihistamine medications and see if they help with your symptoms.
If the symptoms still persist, it would be best to consult an allergy specialist or ENT specialist for your complaints and talk to them about getting a CT scan of the sinuses done.
You would probably need steroid nasal sprays, antibiotics etc.
Let us know if you have any other doubts and also keep us posted about how you are doing.
Hope this helps.