M.L.
I think it's a good idea to get on meds for now. Especially since women who are prone to depression are more prone to post-partum depression.
From my understanding, Zoloft is the safest and easiest to wean from. I have taken depression meds (paxil, horrible) and my sister has taken several, Efexor which had horrible side effects, Zoloft was the best for her.
Fortunately, most fetal development is done by now, so the depression meds risks are mostly to you being jittery or irritable, or early labor. But at 38 weeks, you are considered full term..
I would look up the facts on mayoclinic, it will give you some good idea of side effects and precautions to take (there are two pages):
http://www.mayoclinic.com/health/antidepressants/DN00007