If it's viral, Sambucus (which is an elderberry extract as a cough syrup) does wonders. It's also sold as pills.
If it's bacterial and coconut oil hasn't taken care of it, give oregano oil a try - but be very careful as you don't want to use more than 1-2 drops 2x/day. It's very strong stuff and if you over do it, you can kill the bacteria in your gut and get a nasty Herxheimer reaction. You'd put in 1-2 drops in something else, maybe coffee or tea.
Make sure you take lots of fermented foods afterwards to rebuild gut bacteria. You'd want home made yogurt/kefir, kraut/kambucha/kimchi/pickles, the commercial stuff has some bacteria, but not enough - especially yogurts as they're not fermented for very long.
Be sure to go very low carb as this helps starve out whatever critters are attacking you. Plus things like sugar tend to shut off your immune system for hours on end.
Of course, it could be allergies. If you have a temperature, headache, or other symptoms, and you said you do, it's probably not an allergy - the yellow mucus is a sign of bacteria btw. Try oil pulls with coconut oil, and a drop of oregano oil in addition to consuming coconut oil and a drop of oregano oil in food/drink.
(Oil pull: take a tablespoon of coconut oil, let it melt in your mouth and swish it around for 20 minutes or so and gargle with it, then spit it out.)