Could heavy stress and illness, like the flu cause my period to be lighter? never had sex before

Stress: Stress-physical or emotional-can cause changes in the menstrual cycle. Illness, weight change, emotional upsets are among the stressors. If you have had sex, get a pregnancy test.

Yes -these can be: cause for lighter period. 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.