Why is it so hard for me to get along with people?

I’m not mean. I don’t take advantage of people. I’m actually a very helpful person. But I have very little friends. And it’s hard for me to make more. I was thinking that maybe it’s because I don’t party like everyone else around me. I do know this though..they always tell me I need to loosen up and enjoy myself. And I always honestly am, so I wonder what it is that makes them think I’m not.. I don’t know, what do you think?