You sound exactly the same as I was when I first started at Woolies. During the first 2 months when I was on Checkouts I was working 6 days a week, averaging 45-50 hours a week. (There's no 38 hour rule here) But that was spread over Checkouts, Grocery and Produce. I was top of the 'on call' register (I checked lol) so that meant I was the first person they called to replace a sickie. I think the longest week I ever done was 56, but that was when we had our refit and there were a few of us that worked through the night with the relay team.
However it did all catch up to me, I was sleeping sorta 3-4 hours a day, not eating properly etc etc and it got to the point where I almost broke down, so at that point I said nope, fuck off I'm having 2 consecutive days off all the time. Which I think you need to completely recharge your batteries - to this day I still make sure I have 2 days off in a row.
But those long hours certainly paid off..September last year I was offered the job of Produce 2IC at 16, and at the same time my CSM offered me Super. But at the time the 2IC job was full time, whereas the Sup job wasn't. Plus Produce is a lot more crusier
iMatthew - Have you made your goals clear to your CSM? S/he may not even know you want Sup, but if they do then just make sure you impress the pants off of him/her. You'll get it eventually. What you should also do, which is quite a risky tactic is pick up 1 or 2 shifts in another department, and this could open up your CSM's eyes and be like "Fuck their gonna steal him! Quick let's offer him super". As I said quite risky, but you never know it could pay off