Your periods must have been delayed because of some hormonal
imbalance. Occasionally, when that happens, the next period can be very heavy. The next few cycles usually settle down and you have your normal flow(not heavy).
However, if the bleeding is very heavy, see a doctor. Your doctor will give you medicine to decrease the flow.
Small ovarian cysts are sometimes seen on scan. If less that 3cm in size, it usually resolves by itself and is nothing to worry about.