May I suggest that you avoid the gym for a while? Flying, even on short sectors, can be tiring if you are not used to it. On the facts that you have given us, I'd say you need to go back and take another look at your career move. When you go to work, your employer actually expects you to work !
Mind you, you could always get a job in Crewing or Ops and then you would find out what working long hours is really all about
