You absolutely need to get off this stuff now. It can actually cause permanent damage to the mucus membranes in your nose so I would strongly recommend that you start weaning yourself off of it TODAY. You should also consider seeing a doctor
On Your Own:
1. If you're addicted, you probably can't just stop cold turkey without a doctor's help (see below) so you'll need to wean yourself off of the Sinex by diluting it over several days. Doing that is pretty simple. Buy 3 new bottles of Sinex, a bottle of Ayr saline mist, and a syringe or medicine dropper that has liquid measurements on the side. Wash your hands and make sure you're working on a clean surface. Use a clean paper towel to remove the top of the Sinex bottle and pour out 1/4 of the liquid in the bottle. Replace the liquid you poured out with the Ayr saline mist. Use the 3/4 strength Sinex for a day or two (at the most). Use the same process on the next bottle but dump out 1/2 of the Sinex and replace it with Ayr Saline, and on the final bottle dump out 3/4 of the Sinex and replace it with Ayr.
You should be able to wean yourself off of the Sinex in about a week, but depending on how addicted you are (how long you've been using the Sinex) it won't be easy. There are a couple of other things that will help.
2. Start taking an oral decongestant (Sudafed or a generic version) that contains pseudoephedrine (these are the decongestants that you can buy without a prescription but have to get from the pharmacist - don't bother with Sudafed PE or other decongestants that are out on the shelf and contain phenylephrine, they're not as effective). The 12 hour Sudafed is probably your best bet.
Oral decongestants don't cause the "rebound swelling" that Sinex does so you can take them without any fear of getting addicted.
3. Buy a SinusRinse starter kit and start irrigating your sinuses a couple of times a day - it will feel very weird at first but it will help soothe the irritation and swelling in your nasal passage.
If you can see a doctor in the next day or two, there are two other things that will really help - a short course of oral prednisone and a steroid nasal spray like Flonase (both of which you need a prescription for). Both of these will help minimize the rebound swelling and if you can get the prescriptions you probably won't need to wean yourself off the Sinex, you can just stop cold turkey.
Definitely try to get started today - the sooner you get off the Sinex the sooner you'll feel better.