Littlepolly,
I would discuss this with your doctor - St John's wort is really as strong as drugs such as prozac, so you really shouldn't think that it is safe just because it is a herb. I would doubt that it has been studied in pg women, as not many pharmaceutical drugs are. Clinical trials have shown that it is as effective as prozac and interacts with other drugs in the same way as other drug antidepressants - sorry I'm a pharmacologist and work for a pharmaceutical company for my sins!
However, I was on antidepressants when TTC both times, as the failure to conceive was contributing to my depression, so between my GP and I we decided to keep going with treatment while TTC. With DD, I stopped the day before my BFP, as I had a feeling I might be pg, with the mc, I actually stopped a week before I even had any inkling I might be pg as I was on holiday and had forgotten my tablets.
I suppose what I'm trying to say is that having been there plenty of times, don't underestimate the need to use drugs for your depression, as my GP said who 1st put me on prozac, if I had asthma or diabetes, I would need to take treatment everyday and depression is no different [think this helped DH deal with it all, as he felt it was something he could do to make me better - didn't seem to understand it all at first!]
In both pg, I actually found my depression lifted while I was pg. It was good year after DD was born that I went back on them again and although I'm having very low patches at the moment, I don't quite feel that I'm ready to restart treatment at the moment - I think my low moods are due in part to my upcoming due date and the fact that DH is away in Iraq [it's our wedding anniversary today and I spent the morning, shouting at a well known dealership, why our only just 3 year old car, was needing a new gear box and why one of the doors wouldn't open - looking at a huge bill, thinking why do these things always happen when DH is away?!]
Anyway, sorry, I hope I don't sound like I'm lecturing - please take this as my friendly opinion and experience and above all take care of yourself - you've had an awful past few months . Big {{{{{{{{{HUGS}}}}}}}}}}