I have a thought about your current flare.

The sinus/ upper respiratory issues and
August connection---

Does your car smell musty? There is
An air filter in most newer cars behind
the glove box. Your manual shows how to
open this and replace. my Toyota van
had all sorts of awful plant gunk in it
And even some bird seeds! The dealer
Said this filter gets moldy fast.

Check this out.. As it might be triggering
your sinus issues. Severe sinus pain can
refer to the neck and may explain why
muscle relaxers don't work for you. And
also why your family is showing some
symptoms.