Hi, Fluctuations in the duration and amount of menstrual flow can be seen due to many factors like psychological factors like stress and strain, general factors like anemia, thyroid hormonal imbalance, etc. As your three pregnancy test kits gave negative results, the possibility of pregnancy is less. To get confirmation, better to go for blood test for pregnancy, which can give a more accurate result. If the test gives negative result and if the symptoms persist, better to consult your Gynecologist once, get examined to rule out pelvic or urinary tract infection, which can present with these type of symptoms, and go for investigations like hemoglobin, urine microscopy, etc. This will help in finding the possible cause of your problem and treatment can be taken accordingly. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr. Sree Gouri SR