Never been addicted to smoking (have COPD from COVID, dealt with other addiction outside of that), but second hand, my suggestions are...

1) try to strongly associate all of your worst symptoms with smoking, as in maybe pick up and hold a cigarette when they are happening, or at least repeatedly think, " The cigarettes do this to me." Otherwise, keep the cigarettes out of sight when you are not having symptoms. Logically, you KNOW cigarettes make your condition worse, you KNOW smoking prevents you from feeling better, so see if you can get your brain to understand that this is what does this to you.

2) Stop using cigarettes for nicotine: switch gum and/or patches, or even chewing tobacco. What's killing you is the smoke itself, not the nicotine, though that is bad for you too. If you've been smoking for that long, you aren't going to be able to just quit on the spot without serious and long withdrawal: switch to something safer, and wean yourself off.

3) If you haven't been drinking coffee, you definitely need to start, as taking another stimulant will take the edge off of withdrawal, and caffeine is far less destructive to your body than nicotine. I know that every time I've had to go through drug withdrawal, keeping caffeine in my system has helped me to stay good.

It sounds like you understand the decision you need to make here, and from what you're saying about even managing to stop for a couple days, it sounds like you have the dedication and strength that you need. Sometimes you just need to change your approach a little, work smart not hard.

You can do it!