Am I a Terrible Person?

This is the only place I can say anything, and I need to get it out. This will probably end up being a long rambling, so bear with me (if anyone even reads this).

Two of my sister in laws are pregnant. One just announced it today, and it hurts. I am so incredibly happy for both of them, but I wish it was me. I want to give my daughter a younger sibling. I want to be pregnant again. I can't even walk into the maternity store with my SIL. Again, I am so, SO happy and excited for them, but I can't help but feel jealous. Does this make me a terrible person?