Spotting on and off three days before period then late period heavy bleeding for three days then started spotting again for 2 weeks what does it mean?

Irregular periods. and spotting could mean you may have some hormonal imbalance that could be affected by many different factors, including age, nutrition, illness, exercise (or lack of it), body girth, psychological well-being, stress, season, or simple fluctuations of other related hormones (thyroid for example). It should not be miscarriage if you do not have other symptoms of pregnancy even early on.