OP, give yourself some time. you are in middle school. It's VERY common for girls to have girl crushes at your age. It's common to spend a lot of time thinking about them, admiring their appearance, and wanting to impress them. Girls at your age pay a lot of attention to each other. you are working on developing your outward image, and you need to look to other girls for inspiration, guidance and ideas.
It's also worth noting that middle school is a very awkward time for boys! So it's not surprising that they don't excite you too much. My dd just finished middle school and she never had a crush on any of the boys in her school. She has her celebrity crushes to hold her over until HS.
When I was your age, nobody talked about homosexuals. So it wasn't even a thought that I could be gay when I thought about other girls. You are growing up at a time when gay rights is all over the news and everyone's talking about it. Which is great, but I can see where it would make young kids over analyze their every thought and fantasy.
When you think about these other girls, do you have sexual fantasies about them? If not, and you just find yourself thinking about them, i don't think that means much. When I was about your age, my best friend and I talked about moving in together and even about adopting kids! But just for fun. Lol. We just thought it sounded more fun to live together than with a guy!
Please don't feel that this is something you need to stress over. You are young, and there is no need to label your sexuality at this point. If you figure out that you are gay, I hope you find all the support that you need. Best of luck to you.