1. It varies? Every other month, though, which sucks ass.
2. From about 5 days to a week, at least, I think. My longest was a week and my shortest was five days, so I'm just going on that.
3. I live with all women, so they usually know when I have it since we share a bathroom. But, otherwise, I don't mention it. For your sister, you'll probably know; the first few times I got mine, I whined and bitched about it.