Sinusitis arises from the inflammation of the sinuses with a viral, bacterial, or fungal infection. Many people think that a yellow or green nasal discharge means a bacterial infection, which requires antibiotics but it is not true. It can be a sign that your body is being attacked by either a bacteria or a virus. That said, a yellow discharge does not necessarily indicate a sinus infection. Is your yellow nasal discharge light or dark? A dark yellow mucus can indicate a sinus infection (but again is not necessarily so) while a light yellow mucus can be produced by dry air and a thick yellow mucus can indicate the presence of a "cold" that requires one to drink more water. However, a yellow discharge can also be a symptom of nasal polyps or an allergic reaction to the environment: pollens, smog, house dust, smoke, or chemical fumes, etc. It is, therefore, a must to address an allergic attack right away. Once a yellow mucus has set in and persists for many days, it could develop into rhinitis and those membranes will become very susceptible to other viruses and bacteria entering your respiratory system. I would recommend that you schedule a visit with a primary care physician
or an ENT to evaluate the exact cause of your prolonged nasal discharge.