Please I need help! I’m miserable like this!

I have two best friends and every time I bring up the topic of me feeling left out, they dismiss it and don’t believe me. But when we’re in school if Emma wants to go outside, she’ll ask Amy first and then not ask me and assume I’ll just tag along, but once Emma asked me first and I said yes so then she asked Amy and she said no, so Emma refused to go outside because Amy didn’t even tho I would’ve gone with her. And those 2 always walk next to each other in school and I’m ‘somehow’ left at the back following them. And they have sleepovers all the time without me. I’m so tired of this friendship but I’m so shy and I have no one else to go to, so I’m either stuck in a toxic friendship, or I’m completely lonely. I need help to release my anger, walk away from them, make friends without seeming too annoying, and determine whether or not they’re bad friends. Please help.