Why it's harder around those milestones, I don't know. I experienced something like that right up till about a year.
I've heard some who like to personify the addiction saying, "It's letting you know it's still there and wants you back." I don't know that I hold with that so much as my own inner talk of, "Well, see? You've proven you can do it. Now, why not reward yourself?"
Hang in there, keep doing what you're doing, and just don't use. You'll be okay.
Peace & Love,
Sugah