Difference between 'unfortunately'： 不幸 可惜 遗憾
可惜我的工作要保密: It express your willingnes can't be fulfilled because of irresistible or uncontrolable force, such as discipline,weather etc.

不幸我的工作要保密: 不幸 always relates to death, wounding or very bad things, its use is inappropriate in this context

遺憾我的工作要保密: It doesn't emphasize on your wilingness, but it express your sorrow on the consequnece it caused to other person. in this context, it depends on what may be caused by the confidentialily nature of your job

不幸的是，我的工作要保密: same as item 2