I will preface my answer by saying I have a kind of emotional issue here, so don't mind me if I get too emotive!!

I was a clingy baby. I was just reading through my own baby book that my mum kept and multiple times it mentions how clingy I was. As an adult, I tend to be a sensitive person and get easily overstimulated and like time alone (this sounds icky, but it comes with lots of good stuff too). Its very common for a sensitive/ introverted personality type to be a clingy baby. As others have said, its all down to personality. (not that every baby that is clingy is necessarily sensitive or introverted, just that most people who are sensitive/ introverted were clingy as babies....LOL)

Anyhow, sadly my mum is a very different personality to me and she was not best equipped to understand or deal with a child like me and she kept trying to push me to be more independent. I say push, not gently encourage, which are very different things. As a result I grew up with a shakey sense of security and thinking that my sensitivity was a really bad, shameful thing. I know its a bit simplistic to lay this all at my poor mum's feet, but her response to my clingyness was certainly a contributing factor.

So I guess I am saying, I think clingyness is a personality trait and, as pp said, your response is critical. The mere fact you are posting about this indicates you are highly supportive of your LO, so big hugs and never underestimate the value of your support! Giving your LO a secure base from which she can explore on her own terms is a wonderful gift. You're doing a great job.

Sorry about the lengthy personal post!!