Need Friend Advice

Long story short, my problem is that my friends won't invite me to do anything with them. I'm in my freshman year of high school and I've always had plenty of people to talk to at school, but no one has ever really included me in their tight-knit friend groups. I've never really had a best friend except one girl name Jane, but she was very clingy and obnoxious so I didn't like her. I've always had plenty of friends, but I was never super close to any of them. It's gotten a lot worse this year because everyone's friend groups are getting closer and more exclusive, and I'm not a part of any of them. People will make plans right in front of me and not invite me. A bunch of my friends have a group chat texting message and they talk about it in front of me, but they've never invited me to join it. A bunch of my friends even had a party on my birthday without me, so I just sat at home and did nothing on my 15th birthday while I saw all their posts about the fun there were having. It's only getting worse, and I don't know what to do. Any advice? Thanks.