Rivet
The differance between tiredness and fatigue is worth researching. Sure, you are working shifts and long hours now; however, when you go home to sleep it is in your own bed and more importantly, your own time zone. This is not to be underestimated. Many times I've arrived in a hotel shattered, yet unable to actually get a decent kip because of that pesky circadian rthyhm. ( again, worth a Google as this will determine your life if you go for it).
Believe me when I say I have also worked for a living before flying, but tiredness after crossing several time zones is A tiredness like no other.
Although on a positive note, I enjoy the job and wouldn't want to do Anything else. I can sleep on the plane well which makes a huge differance on long haul. The pay is very good, and I get plenty of time off at home and downroute. I do however work for BA on a legacy contract.
Good luck with whatever your choose.