Going around in circles

I have just accepted a new job. This will be my 7th new job in 5 years. I start out all energetic and raring to go, but in a few months I get bogged down, frustrated, tired, distraught. Then I think the only way to solve it is to start again. How to I break this circle? How do you stay in the same job over a long time? I realise that I'm making my own problems really because the act of starting a new job is so stressful in itself but I really want to make this new job work. I don't think I can cope if it all goes wrong again.