K.,
First, you are NOT petty, you are NOT stupid and you are NOT selfish. The fact that you think of yourself this way proves you are NOT!
Second, you are grieving. You have fabulous suggestions from ReverandRuby and Demetra. We all grieve in different ways. I think you should also try counseling or blogging/journaling. perhaps look into a support group in your area.
My sister is going through something similar. She waited to have kids. Now she is 33 and can't get pregnant. She has been married for 10 years and started trying about 3 years ago. She admits she is jealous of her SIL who is pregnant with her third. SIL is immature and not a great parent already. My aunt told me she used to cry every night, because my mom and her sisters were all getting pregnant and having babies. She kept losing babies. She gave up and finally got pregnant. her baby is now 18 and just graduated from high school! She told me she always yearned for more, even though she felt blessed to be able to have one.
There are other people who have gone through what you have and feel as you do. You are definitely not alone in your feelings and grief. God bless.