Healthline identifies several factors that cause spotting between periods, including hormonal imbalances, pregnancy complications, uterine fibroids or polyps, infection, and the presence of an intrauterine device. Due to the number of possible causes for abnormal vaginal bleeding, it is best to seek medical advice to determine its cause.
Seek emergency medical attention if the bleeding is heavy or accompanied by pain, dizziness, fatigue or fever. According to Medline Plus, it is important to keep track of the number of pads or tampons used, because the rate at which they become soaked is helpful in estimating uterine blood loss. In addition, women experiencing intermenstrual bleeding should avoid aspirin because it could prolong bleeding.