Feel like a Mom

I was just putting my little guy to bed for a nap and I was holding him and rocking him for a few minutes to help calm him down and as I was rocking and kissing him I thought "Why have I never felt like a "mother"?". It's not that I don't love my son, I do, I would do anything for him. I guess I just remember how I always looked at my Mom and how she was just Mom and could do anything. I don't think I feel like I can do anything. I just thought when I had my first child I would have this overwhelming sense of "MOM". I don't, I just feel like me, playing house some days. It's weird. I wonder if I am the only one who feels this way.