Well, this isn't very natural, but it helped me to use one of those twenty-four hour antihistamines ~ like Claritin (loratidine). Claritin D contains a decongestant as well as an antihistamine. I could not tolerate the decongestant because it made me nervous, but if it does not have that effect on you, that is the one I would try.
Once I began using the Clairitin, I stopped developing sinus infections altogether.
The other thing that seems to have made a difference for me is apple cider vinegar in a glass of water three to four times a day. I began using the vinegar to help with acid reflux, but found it seemed to keep my sinuses clearer, as well. I read somewhere that the acidity of the vinegar changes the pH in the throat, making it harder for most bacteria to thrive there, and that this is why the vinegar helps in the prevention of new infections.
Once I get this asthma thing figured out, I will begin using the Clairitin again.
I used a neti pot too, before I started the Claritin ~ it made a nice difference for me.
Those sinus infections are so miserable, Coookie!
I hope you find something that helps you.
Barbara