Why is my period later than normal and why is my menstrual cycle so sporadic?

See a Doctor. There maybe some hormonal imbalance going on which some lab tests can help determine. Also, stress and any changes in diet or lifestyle can affect menstrual cycles. There is something called polycystic ovarian syndrome (pcos) that can lead to sporadic menses. See an obgyn so that they can run labs, possible imaging, and take a thorough history and physical to help figure this out.
Many causes. There are several possible causes of irregular menstrual cycles, and it's imperative to get to the root of your hormone imbalance(s). Some of these are associated with increased risk of health problems. Get tested and then properly treated.