feeling lonely after giving birth

Since giving birth, I don't know why I often feel lonely. It's like... many people don't understand the new sides of me that have emerged. Outwardly, I still laugh, can chat, maybe seem just fine. But deep down... I feel alone in facing all of this. The transition from being a wife to being a mother. It feels really strange to me. My priorities have changed. I become lazy to meet friends and prefer to play with my child. I know it's my choice. But still, it feels lonely... anyone ever felt the same way? how do you cope with it?