What is it? Where is it? Who is it?

Have you ever felt like something is missing in your life? I feel lately like I have a hole in my life or in my heart or in my brain or something.  I don't know why but I just feel like something is out of place.  I feel like something is  missing in my life and I just don't know where to begin to find what this "thing" is. I don't know. I just don't know.