What Causes Periods Twice In A Month?

I am 46 years old. Over the last few months my periods are coming about every two weeks, whereas before were every 28 days. My periods have changed, some very heavy, some light and some as regular as they used to be, both my breast are VERY tender - epecially when I lay down. I don't knwo if I'm hot flashing, but quite a bit of the time I do seem warmer than the rest of my family. Could this be the start of the Change???