Hi Guys. I'm in my 3rd or 4th cycle using my new Mooncup UK size B, my first menstrual cup, but I'm having problems with leaking. When my period is light it's fine, but as soon as it's heavy I find I have to change it every couple of hours, even though it doesn't always look full. It doesn't feel uncomfortable, but I don't think it's sealing properly - it moves up and down, and I can twist it right round, even though it feels fully inflated. Any idea what I'm doing wrong - do I need a different cup, or different size? As I'm only 21 and haven't given birth, I wouldn't have thought I'd be too big...