Sudafed is a good decongestant.
This was recommended to me by an ENT Specialist and I took it for some months.
In my country you can buy it in liquid form to take every four hours. This was good as I cant swallow pills.
I dont really know of a better decongestant. OLBAS-OIL is good as you can smear a little inside your nose or inhale it.
Cut down on milk products as much as possible as they make more mucus.
Have you tried Antihistamines even if you dont have allergys they can help.