Menstrual Cups??

help! okay so I've tried the diva cup in the past but every time I have it seems like it is starting to fall out when I'm wearing it! the stem is sticking out and I can feel it when I walk around and it's really uncomfortable. I've used tampons in the past and I haven't had this problem. I really need to figure this out, bc I backpack and I need a reusable method. I've tried to fiddle with it but nothing seems to work, someone help?