How to differentiate between allergy symptoms vs. chronic sinusitis symptoms. (because sometimes allergy is the cause behind sinus problems!!)?

Allergies/sinusitis: It can be difficult to differentiate. Allergy symptoms usually are runny nose, sneezing, itchy watery eyes, nasal congestion, itchy and irritated throat. Chronic sinusitis is mostly thick discharge, nasal congestion and sinus pressure. Ultimately, it may be necessary to see an ENT allergist or Allergy/immunologist to do thorough history exam, possibly imaging and allergy testing.

Treatment test: Yes, both conditions can present the same symptoms which can make it tricky to discern which it actually is. I would advise trying allergy medication such as Loratadine or Cetirizine and maybe even try a prescription nasal spray. If after a few weeks of taking these you still have symptoms, you may be dealing with a primary sinus issue. CT of the sinuses may help with diagnosis too if meds fail.