Hi,
I know this is an old discussion, but i will post my experience in case anyone finds it useful.
I have had stress problems, minor depression, insomnia, and major psychosomatic problems. In the past I have taken Fluoxetine.
I have been trying with my doctor, mirtazapine 15,30, cymbalta 60, and both 
Mirtazapine, got me out of huge problems with insomnia, when you start it you sleep really really well, negative side effect, I gained 8 kilos. Mood a lot better but sometimes some stress symptoms were worse and the psychosomatic problems were unaffected. I just felt it was kind of wrong for me.
Duloxetin for me is a life savior, i just feel its like I am not taking any medication at all. It is the only that relieved me from psychosomatic problems like diarhea, back pains etc. I probably helps sleep a bit too. The only problem is difficulty in having an orgasm sometimes (ejaculate, not get an erection).
Together they had an even stronger effect in the positives, but mirtazapine is impossible to stop due to the sleep it affects, once I stop it and try to sleep, its impossible.
As a conclusion, taking them together helped in my case, had some sideffects like weight gain and was very difficult to make my sleep natural again.
As mentioned above, duloxetin was life saving.
Its important to understand that these kinds of medication have different effects on each particular person, one may vomit from mirta other may not, one might say its perfect, one might say its the worst experience of his life. In my case I am only taking duloxetin now and never going to take mirta again.
This is why there is always a trial period, trust your doctor but also your body/yourself.
Regards
T