well, you've just turned 30 (milestone); you've got a new baby; you're expecting to get married next year (i'm sure you know that even good things can be very stressful); and you're putting a bit of pressure on yourself (like i did/do) thinking these should be the best years of your life... of course you'll start to feel some anxiety. anxiety will often go hand-in-hand with depression, especially if you've had depression in the past (you're somewhat predisposed to it). however, since you're on lexapro now and you said you've started to feel a bit better (you know you need to give it 4-6 weeks), it's an improvement, right?. and, whenever someone takes meds, i always recommend--based on my personal experience--that's it's really good to also see someone, a counselor, or therapist--that you can talk to about these stresses. they can help you even more in overcoming your anxiety and deep sadness, and maybe coming to a quicker resolution.
much luck to you!!!! and congrats on your new baby!