Do you wish you had more children?

My daughter is almost 15 months and since she's turned one, the thought to have or not to have a second child has become a daily question in my mind. I had such a hard time emotionally after having her and I am slowly feeling somewhat like myself again that the thought of adding another child into our lives scares me. I also just can't imagine loving another as much as I love my daughter- I feel like my heart would literally burst! I also am fearful of her feeling neglected with a newborn. I guess my main question is, those that have only one child and know that you do not want another...do you ever wonder what if? And those that do have more than one, what is the biggest adjustment?