My periods have been abnormal for a little over a year now. they used to come on time. sometimes they r up to a week late, sometimes more. whats wrong?

A few ideas: Your cycle is controlled by hormones produced in ovaries, estrogen and progesterone. These 2 hormones have to be made in right ratios to each to have normal menstrual cycle. When cycle isn't normal can be due to hormones being imbalanced. As well as thyroid or weight issues (being too thin or too heavy). See a dr for evaluation if it's bothersome to you.