What can cause a period to be intermittently spotting of a light color when they are usually heavy but one is not pregnant? what concerns are there?

Abnormal bleeding: Normal menstrual flow should last less than 8 days, needing less than 8 pads per day. No bleeding in between menses. Menses may occur at intervals of 21-35 days apart. Any bleeding outside of those parameters is abnormal and warrants further investigation. Depending on the age and risk factors for the individual, ultrasound, and possibly endometrial biopsy. A sonohysterogram may help stablish abnl