Is it weird that I don't really like to hang out with my friends? Please Help!!?

Okay so let me kind of explain myself. I am very shy and I love art and photography and I am one of those artsy kids. My friends all have completely different personalities. One is a band geek, one is weird and obsessed with Tolkien, one is black and perverted, and so on. For some reason I don't really like to hang out with them outside of school unless they invite me first. I usually never ask them. My mom keeps telling me to get off my butt and hang out with my friends but I keep avoiding it. My summer is sooo boring! I hang out with my sister and my mom all the time. They said they are not my entertainment. Around here there's not that much to do except go shopping, movies, or swim. My friends and I are all 15 and not old enough to drive so that makes it harder. I hate shopping with my friends and there are no good movies, I don't want to go swimming because their parents would have to drive them. My sister keeps making fun of me (she's 18) and it's killing me. I want to hang out with people but at the same time I keep finding excuses not to.