Suddenly short period 1 day spotting and 3 days bleeding first and last day being light. usually period lasts 5-6 days. could this be due to sudden diet change, have been eating less this week?

Maybe. Maybe not.: Many women have occasional variation of their mucus discharge, some spotting between periods, a heavier period, a lighter period, a longer or shorter period, or even a missed period. Having one or two of these symptoms doesn’t necessarily mean there is a medical problem, but a video call to one’s primary care or Ob-Gyn doctor is a good idea if symptoms are persistent, recurring, or worrisome.