Many of us have more complex issues that involve more than one problem. Like you, I have allergies. I also have a lot of postnasal drip, and my nose makes seemingly gallons of clear mucous. Have you tried nasal washings--either with a netti pot or sniffing water from your hand? I use a pint container and add 1/2 tsp. kosher salt (it doesn't have the chemical to keep it from clumping) and 1/2 tsp. of baking soda. I dissolve those in a pint of distilled water. (I guess that ensures that my nose isn't getting doused with chlorine or minerals in regular water.) I then shake it up to mix it well, then lean over the sink. I pour a little into my hand, then sniff it way up into my nose. (You won't get it in your lungs, because you're leaning over, and it comes out your mouth, and drains back out of your nose.) It works great for me, and might help you get some of the mucous out so you're not struggling with it constantly.
I also have had GERD for at least 20 years. My allergist/asthma doc said that reflux can actually effect the nose/sinuses. I ended up getting the reflux surgery (Nissen Fundoplication) because the reflux I got (actually not very severe--and sometimes silent, meaning I didn't know I had it) was causing my lungs to be very unhealthy and inflamed.
The things you're doing are good. My concern, though, is that if you're having reflux, the fruit and tomato juices you drink can be triggers for reflux. You might want to look online for "GERD triggers" to find those foods that can make things worse.
I'm not sure if your sinus issues are caused by GERD, but it could be a contributing factor. Good luck finding answers to your questions. I'm sure others here will stop in to give their opinions and suggestions.
Welcome to the GERD forum!