Hello from a CD who is also a physician, with a special (clinical) interest in the neurochemistry of the brain.

What you are describing is not uncommon with the use of antidepressants, and in fact is sometimes the result desired in particular applications.

Most (but not all) antidepressents reduce the libido, for both men and women.
For the majority of us, our crossdressing is connected with our sexual desire, so it's understandable that your desire for crossdressing might decrease too.

Sometimes the decrease in libido disappears after a few months on a particular drug, sometimes it remains stable. There is an increase in libido (typically) when you stop the medication.

But here is something interesting too: certain antidepressants can profoundly suppress compulsive behaviors. Not just crossdressing (if there is a compulsive element to it), but other behaviors like gambling, phobias, compulsive cleaning/washing, etc.
Sometimes that's a desired effect of the drug, other times it's unexpected.

I read Peter Kramer's book "Listening to Prozac" in which he enumerated some unforseen "positives" from the use of anti-depressant medications.
I was intrigued by his ideas, and started myself on Zoloft.
That particular med has been associated with a decrease in compulsive behaviors, and sure enough I found my desire to dress much easier to control, and not at all intrusive in my life.
I considered it a very positive experience, and stayed on the drug for about 1year.
After coming off it my libido became stronger, but my dressing seemed much less of a compulsion.

One thing I would warn you of, and physicians often fail to mention this to patients.
When you do decide to stop this particular medication, wean off it slowly.
So, if you're taking it once a day, take half a dose once a day for 2 weeks, then half a dose once every-other-day for another week, and then stop.
It is much more comfortable to do it that way than to quit all of a sudden.

Hope this helps,

Chris