My oldest daughter is 9 (she'll be 10 in May) my other daughter is 4 (she'll be 5 in February) as of…

My oldest daughter is 9 (she'll be 10 in May) my other daughter is 4 (she'll be 5 in February) as of now I'm pregnant with a baby girl (5 weeks left due 12/12) this is my husbands first biological child, we want more kids, but I don't want to wait another 5 years. Should I try right after birth or how long should we wait ???