I’m a fourth wheel?

I’m friends with theses three girls and I found out they all have a group chat together that I’m not apart of. They make plans that I’m not apart of. One of the girls we go to parties together almost every Saturday and text daily. The other two we are not as close. We all work at the same job, but I feel like they are closer because they work more of the same hours. When we all work the same hours they kind of group together and leave me out. How do I not be a fourth wheel?