Another baby... when?

It seems like each week I flip flop about having another baby.  The one thing that makes this decision easy is that I still haven't gotten my first post-partum period... Pooks will be 20 months on Jan 9.  Anyways one day I feel so anxious because I want Pookie and her sibling to be close enough in age to play with... the next I am overwhelmed with how much Pookie is still a baby, and how she needs all my attention.  Then some days I feel relaxed and just figure it will happen when it happens.  I wish there was a right answer.