I'm Rh negative, too...
You don't need the rhogam until after the baby on your FIRST baby, I think... but since you've already had one, it would depend on 1) your husband's blood type, and 2) your first baby's blood type.
If your first baby is Rh negative, too, then you don't need to worry about Rhogam until after the baby is born, I THINK (unless there is any kind of trauma). Basically, the Rhogam prevents your body from making anti-bodies in response to Rh-positive blood inside your body. During a miscarriage, abortion, or birth, some of the baby's blood can mix with your body, and your body creates anti-bodies in response.
So, if your husband is Rh-negative as well, you don't need to worry about it. If your first baby is Rh-negative, you probably don't need to worry about it. If your first baby is Rh-positive, then you should get the Rhogam shot before the birth. Your MW should do a screening early, and then maybe one at around 28 weeks, to see if you are already producing the anti-bodies or not (simple blood test).
Basically, you may not even need it, but knowing the blood type of your husband and first baby will help you figure out when and if you do need it-- and your MW will likely be able to give you more exact info in your particular case.