I feel so ungrateful and ashamed of myself. I have 3 beautiful, healthy children yet I don't feel my family?

is complete. I know I am very blessed and so fortunate to have my 3 wonderful children. I fell pregnant at age 23 the first month, fell pregnant at age 24 the first month stopping b/c pills and then fell pregnant at age 28 after 5 months of trying. I have never had a miscarriage or any problems whatsoever with my three pregnancies. No preterm labor, all natural, l deliveries. All perfect, healthy babies. Ever since my youngest was like 2 years old, I have had this overwhelming, and I mean overhwhelming urge/desire to have one more baby. It was all consuming. I could never stop thinking/dreaming about having another baby. I begged my husband for one more baby but he was satisfied with the family we already have. So after many years of begging, I finally wore him down and he agreed to let me stop using b/c and let whatever happens happen. I swore that I would never do anything extraordinary to ist me with conceiving and I haven't. No fertility testing or med's. No BBT checks, no CM checks, or cervical position checks. I just tried to make sure we BD around the time I believed I would ovulate. I firmly believed that if it were meant to be then it would happen. That's been two and a half years ago and it hasn't happened. I am 40 1/2 years old and am coming to terms with the fact that I probably will never conceive again. I feel so ashamed that I feel so strongly about wanting another baby when I read many of your heartbreaking stories about infertility and miscarriages. Instead of appreciating the gifts I have been given, I have allowed and continue to allow this powerful force to make me feel that my family isn't not complete. I feel like something is missing. It is still all consuming and all I ever think about. I daydream about being pregnant and having a sweet little newborn to love. Has anyone else felt similar to this and what did you do to help make these feelings go away? I just want to say to all of you ttc, may god bless you with a little miracle and my heart breaks for you when I read how much effort, heart and soul and has gone into conceiving. Thanks for listening.