It could actually be a little of both, but probably more because of the schedule change. First thing I would do is change to a gym that allows you to lift on weekends. I don't think I've ever heard of a gym not being open on a Saturday.
Also, I understand how tough it is to work 12 hour shifts and still get training in but sometimes it just has to be done. Is there absolutely no way you can train on the 4 days you work?