Bleeding that is not related to your normal period can happen for several reasons, including hormonal changes, vaginal irritation, a small tear after masturbation, infection, ovulation bleeding, cervical irritation, or sometimes bleeding from the urinary tract that appears during urination. If the bleeding is thin and heavy, it is worth paying attention to, especially if this has never happened before. Masturbation can occasionally cause mild spotting if there was friction or irritation, but heavier bleeding later in the day is not always explained only by that. Try to rest for now, avoid further irritation, drink enough fluids, and monitor whether the bleeding is reducing or increasing. Also, notice if there is lower abdominal pain, burning while urinating, dizziness, clots, foul smell, or weakness along with the bleeding. If the flow becomes very heavy, continues beyond a short time, causes severe pain, or you feel faint or weak, getting examined soon would be the safer option. A doctor may need to confirm whether the blood is coming from the vagina, cervix, or urinary tract before deciding on the exact treatment.