20 weeks pregnant

So this is a odd question I know but bare with me. I’m 20 weeks pregnant with my third. My belly is pretty big standing up. In previous pregnancies at this point if I lay on my back I can feel the baby balled up to one side of my stomach. This baby when I lay on my back it completely disappears. I do have a anterior placenta this to round but it’s like this baby is living in my back. Has anyone had this before? I still oddly don’t feel pregnant because I don’t feel him move and can’t feel him in my belly yet.