GMW.....
You're not alone. I'm a freight pilot spending my working life terrorising the skies at horrific hours of the day. Initially I found it very difficult to adjust between work periods and time off. The best strategy by far I've found to deal with it is to stick on one time zone. ie my watch, laptop and phone etc are all set on Zulu time. If I'm down route i don't care what the local time is, I stick to UTC. And as our rosters work in UTC it makes it much easier to adjust to sudden changes.
Is it perfect, no. But it helps. As for going to the gym, I too sometimes lack the motivation when at home but a quick step on the scales after a trip usually sorts that and I'm back on the treadmill like a whippet!