I stopped smoking almost three weeks ago, any tips from former smokers on keeping the momentum going?

I quit the horrible habit cold turkey three weeks ago after smoking ten to fifteen a day on & off for ten years, my cravings are decreasing now & i'm feeling calmer & happier than when i smoked. Any inspiring tips from never having another puff would be welcome : ) ; ) this just seems too good to be true & i'm terrified i may change my mind & relapse : (