Hi, ! First, I am sorry you are dealing with a sinus infection that triggered an MS flare. Second, I don't have personal experience with MS and sinus infections, but since MS is an autoimmune condition, it stands to reason that an overzealous immune response could easily triggered by any number of factors, including a sinus infection. I wanted to share one piece on the topic of infections and MS immune responses that I thought you might find interesting -- https://multiplesclerosis.net/living-with-ms/biological-warfare-fighting-infection-and-ms.
Again, I can't offer much insight, but my husband deals with significant sinus issues and Psoriasis (another autoimmune condition). His flares can be triggered by serious infections, stress, etc.
I suppose your doctors felt like your MS was more of an issue to focus on than the sinus problems? If they were sort of 'triaging' your health issues, I can see why sinus problems might not be considered a priority.
My husband uses a CPap at night and also has had two sinus surgeries. I don't know that the surgeries helped much, but the CPap has been a game changer. That might not be a possibility for you, if you aren't dealing with sleep apnea. The CPap has helped him because the air he breathes all night long is filtered, which gives him a break from any allergens in the air and also tends to help a bit in preventing some (but not all) sinus infections.
I would definitely talk to your doctor more in depth about this and perhaps get a referral to an ENT, if you haven't done so already.
I hope your infection clears up quickly and doesn't return!
Best, Erin, MultipleSclerosis.net Team Member.