Feeling loss even after being blessed

Ok I have Muscular Dystrophy and tried for 12 years to have a baby. I know what your thinking!:) Can she even have kids or sex for that matter? Well, yes I can. I have weakness in all my body getting pregnant was suppose to be not an issue. I had all the tests and finally the diagnosis:Unexplained infertility. I did it all, clomid, shots, IUI and finally I just stopped and needed a breather which ended up for about 5 years. Eventually we would do Invitro once we had the money. I knew since I was 14 I was meant to have children. I am a preschool teacher and I raised my little sister since a baby. It got to the point where I couldn't go to baby showers anymore and cried when I saw a pregnant person and it seemed like everyone around me was pregnant. Well finally without warning or even trying I got pregnant. I now have a healthy miracle 4 year old Son. He is everything I could ever ask in a son. He is sensitive and he listens before I even get to the number 3. (ya know 1...2....3:)) anyway, I know I am lucky, but I still feel sad when ever I see a pregnant person or a little baby. My counseler says i was tramatized by being dissapointed for 12 years. Shouldn't I be content and happy? My best friend who is now 41 chose to wait to have a baby because she felt pressured from society and only now was trying because she thinks thats what you do. She wanted someone to take care of her when she gets old like she takes care of her parents. So on her first try she gets pregnant. I am happy for her but still sad for me. No one I know understand what I am feeling. Not even my husband. I am now 35 and want to have another baby and my sadness just does not seem to go away. My sister called me selfish because I expressed I didn't think I could handle going to my friends baby shower. Am I selfish? does anyone understand my feelings? Why can't I just be content?