3 days late but had light bleeding of old blood for three days. Always have heavy regular periods? 3 neg. Hpt a week later. What could cause this?

A one-time symptom? Many women have occasional variation of their mucus discharge, some spotting between periods, a heavier period, a lighter period, or even a missed period. Having one or two of these symptoms doesn’t necessarily mean there is a medical problem, but a visit to one’s primary care or ob-gyn doctor is a good idea if symptoms are persistent, recurring, or worrisome.