If you're really concerned about having the chemicals in your body while pregnant & breast feeding, and it's an SSRI that's working for you, you might want to consider switching (gradually) over to a 5HPT supplement. That's what I did to wean myself off SSRIs the last time (not for TTC, but because I just didn't want to be on the SSRIs anymore), and I go back to them when I feel like I'm slipping.
SSRI = Selective Serotonin Reuptake Inhibitor. It is believed that they work by preventing the neurons that send Serotonin out from taking it back in when it isn't received fast enough, allowing more time for signals to be transmitted via this particular neurotransmitter.
5HTP is the natural precursor to Serotonin (5HT), so by taking this on a regular basis, you'll eventually increase the amount of Serotonin in your brain, which can lead to the same result. More Serotonin to be received so that reuptake takes longer, instead of turning reuptake off.
Since it's already naturally occuring in your body, and not an artificial drug meant to alter the way your brain works, it's not something to worry about passing on.