Suckling just like baby??

Koda
I just had my baby a few days ago. I've noticed that I've started to suckle/ suck on my bottom lip (like the baby does) at random times. It seems to happen involuntarily and I really have to focus to make it stop. I get a very strong urge to suckle, which feels similar to the rush of hormones I get while breastfeeding.
Is this normal? Does anyone have a theory as to why it happens?