I quit cold turkey when I got my first BFP a little over a year ago. The first 2 weeks were he!! But the motivation was there. I later lost that pregnancy and it took all my will power not to go back, but I just couldn't in good conscious while TTC. I obviously wasnt drinking at the time of quitting, but I did after the loss and I was able to drink and not smoke, though it was a trigger for quite a while
It's really about internal motivation. You have to want to quit, and you have to remind yourself everyday for months Why you quit. Eventually, you'll stop thinking about it daily and it will be a few times a week, then a few times a month, etc. It will happen if you want it enough, I promise!!
Congratulations on four days, that's a huge step!! The first two weeks are the hardest : if you can get through them, you can get through the next two weeks, and the two weeks after that, and the two weeks after that