The pattern of bleeding you are having occurs in anovulatory cycles. These are cycles where in there is dysfuntion and irregularity in egg release from ovaries which are responsible for the disbalance in hormones. This manifests as delayed periods which are then heavy.
The most common cause in your age of these cycles is Polycystic ovarian syndrome
where in there are irregular periods
, pimples, unwanted hair on body and face and excess weight gain.
It can be diagnosed by a hormonal work up along with ultrasound.
Treatment includes metformin with oral contraceptive pills
The other possibility can be a thyroid disorder
. It can also manifest with irregular heavy periods. Depression, fatigue and mood disorders also occur. Blood test for TSH LEVELS is used to diagnose the same.
You should meet up a gynecologist and get these two possibilities ruled out and start the appropriate treatment.