It is time to see a doctor when they can help you with one of the following:

Prescription Medicines: Some of the safest, most effective medicines are available by prescription only. You might be surprised at how much relief is available when the correct medicine is used properly. If you aren't getting relief from over-the-counter medicines, or if they have too many side effects, you should see a doctor.
Advice based on experience: Doctors see this stuff all day. They know what works for people and they know what doesn't. General information, such as given on this site, is a great starting point; but when the most common steps don't work well, its time to seek out experience. Knowing what exactly is going on and what is best to do for it can be very complicated at times.

Diagnostic studies: When it isn't clear exactly what the problem is, doctors can use examinations and tests to help identify the problem. Physical examination using special lighting, microscopes, or endoscopes is the fortes of your ENT specialist. X-ray and CT scans are an integral part of the workup for more difficult conditions. Allergy testing and occasionally laboratory tests can all aid in helping diagnose difficult sinus and nasal problems.

Which type of doctor should I see?

Primary Care:

When problems are intermittent and relatively mild, a primary care provider is a reasonable first stop. From your history and physical exam, your doctor will help you determine what the likely nature of your problem is, and a reasonable starting point for managing the problem. Primary care providers are an excellent resource for acute infections, common nasal allergies, and to help direct you in the next directions if your problem is especially difficult.

Ear, Nose, & Throat Specialists:

ENT doctors are expert in the evaluation and treatment of difficult sinus and nasal problems. Some ENT doctors, such as Dr. Casano, have special interest within the field and concentrate on sinus and nasal disorders. Since ENT doctors have experience with treating allergies, infections, and surgical nasal conditions they are the single best starting point for difficult sinus problems.

Many people think of ENT doctors as surgeons, and while this is true, the majority of patients who see an ENT do not end up having an operation. Carefully selected diagnostic and treatment plans benefit patients with severe allergies, chronic infections, airway obstruction, and other nasal disorders.

For some patients modern surgical techniques are the only way to get full relief. Your ENT doctor can advise you on these options. Many problems that patients thought they would have to live with can be corrected with minor surgical procedures. ENT doctors are the only doctors who can fully discuss all of the available options with you.

Allergists:

Allergists are trained to test for what you are allergic to and treat these with medicines or "allergy shots". If your problems are frequent or severe, and if you aren't entirely positive that the problem is all allergy, I recommend that you see an Ear, Nose, and Throat doctor.  I refer patients to the Allergist when allergy testing and allergy-shots are appropriate.

ENT doctors are trained to help you decide what your problem actually is and treat the problem regardless of whether it is allergic, anatomical, infectious, or other.   When it is clear that allergies a significant part of you your problem and when the simple first measures haven't been effective: then it can be time to see an allergist.