Would allergies n stuffiness cause lightheadedness 24/7 for 5 yrs daily basis or could it be a neurological condition

Not usually: Allergic disease of the upper respiratory tract does not usually produce persistent lightheadedness for 5 years. I am surprised that you have not consulted a physician. I agree that a neurologist would be a good idea but there are many medical conditions that could cause light headedness, such as low blood pressure, low blood sugar, low thyroid function. You need a good medical workup.