How can I tell the difference between nasal allergy and sinusitis

Associated symptoms. Persons with nasal allergy typically have congestion, clear nasal discharge, itchy and watery eyes. If symptoms last more than one week, a viral cold is unlikely. If the drainage changes to anything other than clear, it may be infected (sinusitis). Colored drainage suggests infection, but clear drainage does not rule it out. Many allergic symptoms are seasonal, but not pet or dust mite allergy.
Daycare kids. Young children are often mis-diagnosed with nasal allergy and may carry long lasting sinusitis. Daycare bacteria may be antibiotic resistant and many physicians give-up on treating infections after using 3 or 4 standard antibiotics. Nasal cultures can be helpful in these situations, especially if wet mucous is available in the nose or can be blown out into a tissue.
Colored mucus. The most tell-tale sign of sinusitis is colored mucus (yellow or green). A pure nasal allergy should only yield clear/white mucus. Also, sinusitis typically causes sinus tenderness over the cheeks and forehead (over the eyes). However, allergies can cause sinus pressure as well. Finally, some people develop fever, chills, and/or sweats with an infection, but it is not as common with sinusitis.