I never connected sinus with Mirena either! Drugs.com lists as side effect of levenorgesterol IUD.
For me while Mirena was inserted - no mucous, feeling of fuzzy, hot, cotton wool stuffed up my nose and into my jaw and a killer headache. I tried to tell the doctors but they looked at me as if I was an idiot! I lived on antihistamines for Mirena itch so maybe that stopped the mucous I associate with sinus who knows?
What a fool to put up with this and more for 3 1/2 years. The positive of no period also made me overlook many horrid side effects, it was not until they got life threatening that I had it removed. - anyway back to topic, I hope I can be of some help to you or someone else.
I am now 4 mths post removal sinus/nasal issues seem to have cleared, what I did and how I felt after removal follows.
Initially much worse - don't be discouraged.
Nose - almost continuous for 3 mths - snuffly blocked on one side or the other, felt red raw/chemical burn inside nostrils up to bridge of nose, cartilage felt bruised between eyes. Only comes back for a few days here and there now. Hormonal crying was a godsend to clear things out!
Ears - blocked, crackled, creaked, rumbled continuously - quite unpleasant, only came post removal.
Relief 3x daily - sinus, pressure point massage (youtube search), blocked ears - swallow hard three times then hold nose and swallow three more times - hard to do but persist it is really worth it! (Mr Google - blocked eustachian tubes).
One day the light will come back on in our worlds, for some it takes a little while to reach full power but it will shine brightly again. Stay safe and fast healing - Bev