I have had a ventilation operation having had to endure months of beconase allergic rhinitis shite before I got near an ent surgeon.
I still suffer 25 years later.
It used to get into my ears and I'd feel as if I was about to fall off my chair. Only then would the GP give me antibiotics - 1994/5.
The is a treatment that means you avoid antibiotics, sudafed causes rebound congestion but only if you aren't on medication for hypertension AFAIK.
It's n-acetyl cysteine - sold otc in France 200mg sachets 1-2 up to 2-3 times a day. I used to go into a pharmacie at the end of my holiday and buy 10 boxes - dd suffered with glue ear.
I've just suffered for 10 days had antibiotics 'in stock' from 2019 still in date. My GP gave me a prescription for new ones 2 x 2 per day, told me verbally to take the old ones 3 x 2 per day, I had tramadol for the pain and, as I've got a thyroid problem gave me a pre-emptive strike of an anti-thrush pessary jyst in case.
I buy a flat bottle of n-acetyl cysteine on amazon. In 600mg capsules. When the weather is unsettled north/south and continental/Atlantic systems I take 2 x 600mg every morning until it clears and don't stop until the weather settles. They also give prednisone tablets which stops the swelling in the nose.
Inhaling menthol crystals in boiling water with a towel over your head might help. I have very sensitive skin and would rather pour acid on my face - I've had skin turn black and drop off from conc sulphuric acid burns.
Inhaling olbas oil in the same way can help as will Olbas oil pastilles.
If it's something you get after a cold put a few drops on your back and front to help prevent it while you sleep.
When the borders open you can buy an otc remedy called Euvanol makes me want to heave, but it does work. It contains the oil from generanium leaves, depends how you feel about that - for me it's not a plant smell but an obnoxious odour, prefer pig slurry personally. It comes in one of those bottles like beconase etc stick the nozzle up your nose, with your fingers on the little flaps and give 2 good squirts. (shudders)
Mine is above my eyes - I don't get toothache as you do with the cheek sinuses. Pressing and massaging as hard as you can bear with the heel of your hand on the 'top' corner of the eye socket rub in little circles.
Joy of joys I'm free of the sinusitis problem but am still taking tramadol some randy sod out on unknown roads having made a rdv on a hookup site cruised passed me driving in the middle of the road - we give them the 180 ° death stare - anyway he was trundling down the hill - I live at 400m - passed the name with a line through it I kept a safe distance. Suddenly without any warning, no indicators, hazards nothing he stops in the middle of nowhere to look at his mobile phone on the seat next to him. I stopped in time everything fell into the footwell but I didn't hit him. I have arthritis in my neck due to broken spines, my neck is rigid out to the point of my shoulder over the 'hook' on my shoulder and all the muscles between my ribs were in spasm later that evening
If, when borders are open, please get someone going to France on holiday to get you some Euvanol. It might might just be sold on Amazon.fr
Sinusitis is a bitch, I prefer childbirth personally, but that's just my experience. In France it's 4 days before they treat you. I have been known to lie about the time when I know I need the steroids - it's the only way to get past the receptionist to get an appointment. Especially before the weekend/Monday morning.
In your place if you've tried everything else I'd be tempted to have a memory lapse and make the start date 3 days earlier.
Best of luck