You've clearly had a hard time in the job hunt and I would suggest that you take a short time to focus.
I don't know how much information you have put on your CV about your previous careers, or how long you were with any of them, but if I was looking at your CV I would be reluctant to employ you also because of your inconsistent work history. You have also clearly stated that you don't know what field you are interested in and if you are suggesting this in your cover letter or CV, even by omission, you will not be selected for the next level.
I would suggest that invest some time in working out what you want to do. What are your interests? What motivates you to get out of bed in the morning? Do you enjoy singing? Teaching? Working with animals?
Then take some time to jot down the things that you are already experienced in and/or good at. What skills do you possess that could benefit someone else (there must be lots if you stuck it in the army for even a short time).
Once you have put these things together try to form some sort of job role that matches these. Once you are motivated to find a career that you think you would really enjoy, you will find that this shines through in your application form and is likely to be noticed by employers. Don't just go for the first thing that's out there, work out what you want to do then pick up the phone and speak to prospective employers.
If you get stuck at any point in the above process, please let us know and we'd be happy to help you some more.