Why do I want a baby so bad?

3 months ago my boyfriend and I thought we might be pregnant but it turned out to be a false alarm. We were both relieved but soon after I realized that I was hoping I was pregnant. We are no way capable of having a baby so he has told me no multiple times. However, I’m depressed. I feel like I need a baby in order to be happy. Whenever someone brings up a baby or I see one, I have to fight this heartbreaking pain in my chest. I’ve tried to explain how I feel to my boyfriend but he just doesn’t understand my pain, I feel alone. Has anyone else experienced this? I just want some relief.