Spotting to light flow x5 days instead of normal cycle. what could be cause? neg preg. test.

Probably normal: Some women will have lighter or heavier periods depending on a variety of factors. Your stress level can certainly affect it, including but limited to missing a period or having a lighter or unusual period.

Could be normal: This very well could be normal. It is not unusual for women to have a little bit of variability in their menstrual flow, especially if you have been under any recent physical or emotional stress.