On my last cycle (which was my first since 2006 due to pregnancies and lactational amenorrhea) I tried a large Lunette. After feeling like it was falling out of me all the time, cutting off the whole stem and getting extremely frustrated, I just gave up using the cup for that cycle. After reading this site, I realized I have a short vagina/low cervix, and I used the cup size chart to choose something else. I selected a small Lunette for its relative shortness and good capacity. I started my period yesterday and used it during the end of the day and last night. Everything was good. I used it this morning, and again, no leakage. The cup was filling quickly due to my heaviest day and the fact that my cervix has to sit in the cup. Even still the stem is right at the labia, but I don't want to cut it. Then I decided to go for my 3 1/2 mile run with the cup. Not even 1/2 a mile into the run the cup was falling out! The stem was folded to the side, and I suppose my underwear is all that held it in. I was wearing dark running tights, so I just kept on and finished the run. When I got home and took the cup out, it was full of blood. I continued to use it until this afternoon when the "lowness" of the cup just got on my nerves too much, and I took it out. Is it possible that my cervix is just "too low" for cup use for the whole of my period including during exercise? Are there other cup users who find that how low they HAVE to wear their cup is just annoyingly low sometimes? I know it can't go any higher because I have felt all around in there, and I can reach all sides easily with just my index finger.