Any other Stepmoms out there TTC #1??

Hello everyone!  I was wondering if there are any stepmoms out there TTC their first.  I have found there is lots of extra anxiety and social opinions out there when you are TTC #1 and DH is TTC #2 (or more).  DH and I have been trying for 18 months and I am starting to find it hard to set aside the jealousy of family and coworker's pregnancies.  I am very involved in my stepson's life and I love him so much, but the desire to have a biological child is sometimes so strong I find it difficult to hold myself together.  My In laws talk with me as though I am his mother (it was not an amicable divorce, we only see/communicate with his mom if she doesn't have a choice), which is painful since I strongly believe that my place with my stepson is as a loving adult that he can trust and will direct him in the right direction but never a substitute/ replacement for his mom.