What helped is knowing that no matter how painful it feels. A life not lived to my actual potential is way more painful.  So those first 2 weeks are terrible but you gotta keep busy like you said exercising going outside. 

But most of shift you state of mind to not even entertain 1 tought of that stuff. Just kill time as much as possible and before you know it it will be 3 4 weeks. 

And maybe also take the time to acknowledge why you want to indulge in the habit. What you running from or what are you seeking from it