It sounds like you are not shy, but afraid to be yourself and open up because you've been bullied.

I was bullied as a kid. I was sickly skinny and had a huge nose. There was a group of popular girls who were mean to the kids who they decided weren't cool. I was one of them. I used to come home from school every day crying. Any way I tried to defend myself only infuriated them more. Eventually, I moved away. There were nicer people in my new schools, and I was never bullied again. It was an awful experience, but through it I learned to be very friendly to new people I meet. I always look people right in the eye and say 'hi' and act like I am really well adjusted to compensate for that feeling you are having of withdrawal.

Sometimes I make friends and sometimes people still don't like me, but I always act friendly and welcoming, like I am very self confident and open (even though I am really not).