no regular schedule

I'm about 5 months into my first nursing job on a monitored bed floor in an acute care hospital and am growing discouraged by the lack of quality of life and stress & strain on my family by not being able to plan anything with them. Though I'm thankful to be employed as a new grad with good pay & good benefits, I have no predictable schedule other than that I work 12-hr nights. Most of the time my schedule isn't released until less than 2 weeks before I am required to work. My manager is a pleasant person, but he has delegated work scheduling to one of the night nurses and doesn't like to confront people or get involved after he has delegated a task (by his own admission). The scheduling nurse is not receptive to my requests to be placed on one of the two night teams, so I can know more predictably when I will be working. Instead I am being used to fill in wherever needed, which means if someone on one team wants a night off, then I am switched to that night, back & forth. I am scheduled to work overtime without being asked, and my schedule is changed without anyone telling me. I literally have to check every time I go in to work to make sure that I haven't been "written in" to the book for the next night without any notice. When I have spoken to my manager about this, he says that it's hard to cover all of the scheduling needs and that "next month it will probably get better" because so-and-so will be back from being out sick/having surgery/on vacation/on family leave/etc (endless problem list & excuses - I don't see any end to this).

Does anyone else reading here have experience with this problem and/or can offer me some constructive suggestions?