I took 20mg of lex throughout my third pregnancy. There is risk particularly with heart defects and other potential birth defects along with delivery complications (early delivery, etc) but those risks also run with depression/anxiety. Work with your doctor and do what you feel comfortable with. You may find adding Omega 3/6/9 to your routine to be helpful. I know I did and there are a lot of women who have as well. Omegas have been proven to help with depression. B vitamins are great for anxiety. Check with your doctor before adding both - too much B vitamin can cause some really nasty side effects so you want to be sure you're not taking too much. (check your prenatal vitamin to see how much you're getting daily)
As far as anxiety, you would want to focus on slowing things down. I know that's hard with a three year old (and I really do, I have a 5yo, a 3yo, and an almost 2yo!) but if you can put your 3 yo in a safe place (like his/her room) while you go lay down and breath slowly for about 10 minutes that would be helpful. when you breathe, breathe in through your nose filling your ribs outward. when you breathe out, do so by tightening your abs and releasing the air slowly through pursed lips. If you cannot separate yourself from the three year old, I would recommend putting together an "escape kit" full of toys he/she only gets to play with when you really need a time out. Put a favorite cd on your computer or mp3 player (if you have one), put on headphones and zone out for a few minutes. Keep an eye on the kid but you won't be able to hear them. I have found this to be great on the really tough days. (I use Pandora though - Last fm is supposed to be really great too - these are both free internet radio sites you can find through Google)
Another thing that many women do to deal with anxiety is to distract their minds. Start listing the 50 states, capitals, types of fruits, vegetables, colors, types of cars - anything to get your mind started in a different direction.
you can also change your diet to help deal with anxiety/depression. A great resource for eating to keep depression away is: www.rebuild-from-depression.com/blog. Another resource I want to recommend is Pregnant on Prozac by Shosh Bennett. It's a terrific book which really focuses on natural solutions for depression/diet. You can get it through Amazon.
I'm glad you stopped by and look forward to sharing your journey! Please do not hesitate to ask any other questions, share concerns, or just keep us updated as you can!
Warmest,
Lauren