I get more clumsy a few days to a week before my period - dropping things, bumping into furniture, etc. is there a scientific explanation for that?

Yes: Just before your period, your estrogen and progesterone levels drop dramatically, changing your brain chemistry. This can cause all sorts of symptoms, among them slowed reaction time, fuzzy thinking and clumsiness. (As if bleeding weren't bad enough!) If severe, these and other symptoms are part of the Pre-menstrual syndrome (PMS). Best wishes!