Side effects of some medications
Many drugs are known to affect the capacity of the blood to clot. Aspirin and anti-inflammatory drugs such as ibuprofen, for instance, affect the role of the blood platelet which contributes to easy bruising. Other medicines, such as corticosteroids and pregnancy prevention pills, often cause blood vessel inflammation, sometimes leading to blood leakage, which is manifested as a bruise.
You can also know what is probably causing your bruises depending on where they are located.