Hi Alexandra, welcome to Healthcare Magic forum. If periods are regular, a day or two more or less is not a major issue. But if you have pain on the right lower abdomen or pelvic area you need to see a surgeon or gynaec immediately to rule out appendicitis
. It may even be a sign of an ectopic pregnancy
, or abortion
,as pregnancy maybe associated with scanty flow. You need urgent ultrasosngraphy and other investigations. Do consult a doctor as soon as possible.