Making friends (Barcelona)

Hi everyone!
I'm new to this site and thought I should get started by posing a question.
Have any of you had trouble making friends here in Barcelona? I've found that after 3 years here, I have very few friends, and they're all foreign! It makes me wonder about cultural issues... do people just not need to make new friends, since they're still pretty much hanging out with the same group they met in grade school? Or is it something else I've missed?
(For what it's worth: not only am I American, but I'm from the Midwest, where people are really open.)
Please share your thoughts!
Thanks!