Some girls have mild cramping the first couple of days of their period and/or a twinge-like pain when they ovulate, but this discomfort should be relieved with over-the-counter pain medicine such as ibuprofen, not last long, and the pain should not interfere with your daily activities including sports.
It’s difficult to know for sure what is causing your symptoms, but keeping track of your menstrual cycle and writing down when you have cramps and/or nausea or other lower belly symptoms along with nausea and/or vomiting can help your provider make a diagnosis. Plan to make an appointment with your provider and bring your menstrual cycle diary with you. It’s important to tell your provider if you are sexually active and if any women in your family have endometriosis. If you have sharp severe pain on either side of your lower belly along with nausea and/or vomiting, call your health care provider right away; rarely this could be a sign that your ovary has twisted or appendicitis (right-sided pain).