Lightly bled off and on for 3 days. much shorter than my 5 day cycle. from pink to red. but neg. pregnancy test 1 day after it ended. was it ib?

Light period.: Not sure what you mean by IB. Was this the time of your normal cycle. The main reason for light periods is a change in hormone levels. Causes for what seems to be a light period can include: implantation bleeding in early pregnancy, thyroid problems, eating disorders, excessive exercise, initial periods for a girl, use of an intrauterine device, oral contraceptives & perimenopause.