My body is so confusing!!! Help!!!

Atlantis
So my last cycle was 7 days late then AF came and she was short and lighter than the usual. AF is usually 7-8 days long with mostly heavy days. This time AF was 5 days and didn't use as many tampond as usual some days I used liners I don't think it was implantation bleeding but before AF came I started using prenatal vitamins. Could that have changed it or is it something else?