Hello and welcome to the forum. I hope that you are feeling better! Please see your doctor. However, in general, it is a myth that bright or dark yellow nasal discharge absolutely means bacterial infection. Both viral and bacterial issues of the upper respiratory tract can cause this colorful snot. So, it could just be a common cold as well. Do you or did you have any other symptoms such as fever? How about when you cough, does mucus come up? Or does it drain down the back of your throat? A general rule to follow is if you have been sick for 10 days or more, it is time to go see your doctor if not sooner. Here is some information on sinusitis and how it is diagnosed. https://www.webmd.com/allergies/sinusitus-test#1 Let us know how you are doing!