Some advise?

First day of my period was yesterday, and usually I have very heavy periods and always have been since I was 16, followed by cramping causing me to faint or something nausea. But this month it's changed dramatically, I have slight cramps in my right side and towards my back, very swallon and sore breasts and very little bleeding.!! Does anybody know what might cause this to happen?? I've taken a hpt and came back negative, so I know I'm not pregnant. X