When a woman gets around her mid 30's, she will sometimes have hormonal changes that can cause most of the symptoms you've been having.
During the 30's it's also not unusual to skip an ovulation, which can result in irregular bleeding. Usually regular 28 day cycles mean regular ovulation, but sometimes not.
If you get any prolonged bleeding or spotting again, then I would see your doctor for evaluation. Some hormone pills will likely resolve the abnormal bleeding.
Stress is often a precipitating factor as well, so I would try to deal with any stress in your life as well as possible.
Eating well, getting exercise and sufficient sleep are all recommended. If you continue to have problems, see your doctor. Best wishes.