Hi, Minor fluctuations in the flow and duration of menstrual period can be seen frequently due to many causes ranging from physical, psychological and hormonal, etc. The collected blood in the uterus can come out as a gush and dark in color during the passage of urine due to increasing the pelvic pressure. Some amount of abdominal pain is common during menstruation, if the pain is severe and not getting reduced with regular antispasmodics, the possible causes are: -Pelvic inflammatory disease -Endometriosis -Fibroids, adenomyosis, though rare to your age. If the pain persists or increases, better to get evaluated. By clinical examination and ultrasound, the possible cause of your problem can be identified and treatment can be taken accordingly. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sree Gouri S. R., OBGYN