I feel your pain. I had similar experiences until I left the 135 world and rejoined the 121 ranks. Having a schedule with work life balance is crucial.

I second myface's comment; will power is all you have available to you right now. However, it also helps to find something else to do with your layovers besides eat and drink. Get a hobby, read a book . . . there's a reason lots of grey haired pilots have big bellies too.

Personally, I got back into running a few years ago and it has made a huge difference.