This can be somewhat difficult to differentiate. Of course, allergies are not contagious, but since you do live in the same envirornment, you're all being exposed to the same environmental allergens. This can be anything from pollen to mold, dust mites, pollutants that might be in your area, pet dander, etc. As the concentration of the allergen in the environment becomes more concentrated, the reaction will, of course, become more severe. All of the symptoms you mentioned are very typical of these common allergies. Though simple over-the-counter antihistimines work for some people, for others, this may not be sufficient. Prescription-strength medications, including decongestants and corticosteroids, leukotriene modifiers (which block immune chemicals that cause the allergic response), and mast cell stabilizers (which prevent the release of histamine in the first place) work very well for severe cases.

Of course, the other possibility sounds like either chronic bacterial or viral sinusitis, which is also typically accompanied by similar symptoms. If you live in very tight quarters, it's possible that you all may be passing an infection back and forth to one another and reinfecting yourselves. Obviously, infectious sinusits would need to be treated differently than allergic sinusits, using antibiotics in the case of bacterial infections for example, in addition to decongestants.

There are a few ways to tell the difference here between sinus infections and sinus allergies. If there is any green or yellow or foul-smelling nasal discharge or sputum (particularly, for more than a week), this indicates an infection, rather than an allergic reaction. Though both infections and allergies can cause pain in the sinus passages, infections can lead to a buildup of fluid, which can cause a sensation of severe pressure, and this could indicate an infection as well. Green or yellow discharge from the eyes, or really thick mucus in the chest with a cough is more indicative of an infection, and not simple allergies. Usually, there is no cough and heavy congestion with allergies. Either allergies or infection will cause fatigue, but allergy fatigue is more mild, whereas fatigue with infections can be severe. The biggest indicator that can be used to distinguish is whether or not a fever is present. In the case of common allergies, there should not be a fever, however most infections are usually accompanied by at least a low grade fever (normal temp is about 98.6 degrees F).

Also, your doctor can determine the cause of your symptoms through blood tests or sputum culture and analysis. If it's found to be allergy-related, skin tests can be performed to determine what allergens are affecting each member of the family, and which medication is best to use. From your description, it does sound very much allergy-related, however. If over-the-counter benadryl or claratin, and decongestants do not help in relieving symptoms, you should see about a different approach from your doctors (including the meds mentioned above), and screening for bacterial or viral causes.

You can read more about sinusitis here (both allergy and infectious): http://www.ehealthmd.com/library/Sinusitis/SIN_whatis.html

I hope this helps, and try to enjoy Memorial Day through the sneezing! Images available only to Customers.