Here is the best advice I can give you. You start again from day zero, but you have to learn something from your relapse. If you learn something than it is not a failure. Learn, why it happened, when, how? (was it worth and how you feel now-we all know the answers to these questions). IF you know why you will be able to prevent it next time. An example from my own experience. A few months ago, I was relapsing right after day 3, every time. Every time in the mornings. So I learned that I am weak in the mornings and I created a new habit. Getting out of bed the second I woke up. I didn't relapse for more than three months in the morning and I never will.