Melissa,
You are entitled to your feelings. The other ladies have good points but these are still Your feelings. You want to find ways to work through them.
I thought it was wonderful you said "My husband and I have 2 children from his previous marriage..." It sounds like you have embraced these children while at the same time understanding they have their natural Mom. That's great! To help yourself get past these feelings of jealousy of what your husband had with his first wife I'd suggest talking honestly with your husband about your feelings. Don't whine or stomp your feet. Just discuss it. If need be see a counselor a couple of times to get some tips or ideas on how to work through this.
Keep in mind most people have relationships before they get married. You may have had relationships before you met your husband. That's okay. It helps you to learn and grow and figure what type of person you wanna be with.
Try not to focus too hard on a baby. It may or may not come. But you can still experience life, learn and grow. Sounds like you have a pretty nice family.