Menstrual Cup Issues

I finally tried a menstrual cup and I can not figure it out!! I don't know if I have the wrong size or what. I know I'm not getting it in far enough but I literally can't push it any further and it won't suction so I stand up and my muscles just start slowly pushing it out until the end is sticking out and I know that's not supposed to happen. I'm a small woman and I have had vaginal birth but I ordered the June cup XS and S because I just felt like the large they recommend for mother's would be way too huge. any advice from the pros would be great!