I was offered a promotion which I accepted and now regret. This was really the formalisation the level of work I was already doing with some additional responsibilities. Before accepting I raised concerns about workload saying that I was already struggling and would not be able to manage current work plus the additional work. I was assured support would be put in place that I could delegate to but this has yet to happen and I am now being told it is unlikely to happen in the near future.
The additional work has also turned out to be a lot more than I was led to believe. I think I've been stitched up 
I have worked there for a long time, I was very good at my job and respected but now I feel rubbish at my job and that l am letting people down. I have given it my best shot, tried to be positive and put in extra hours to try to make it work but it is now starting to take a real toll on the rest of my family life and my health. I work late, I am mentally drained and exhausted when I get back and cannot switch off. I wake up in the night thinking about work and because i am not on top of things I find myself going in early and staying late. I have tried to raise this with my manager and was just given some corporate fob off nonsense about delegating and streamlining process and things in the pipeline blah blah essentially putting it back to me.
DH is supportive but concerned about me carrying on line this. If I work out the additional hours I am doing the increase in pay doesn't come close to covering it.
Can I withdraw from the promotion while still in the probation for the role? I think I might have to for the sake of my health and sanity.