I'm having sever pain in stomach with a period also passing blood clots the size of eggs and stomach is swelling also 12 days between last 3 periods?

Not normal: A change in your menstrual pattern can sometimes occur but bleeding every 12 days with large clots and severe pain is not normal. See your doctor as a pelvic exam and/or an ultrasound may help determine the problem.

Agree With Dr. S: You have excessive blood loss and should consult a gynecologist. Start taking oral iron and multivitamins to prevent anemia due to iron deficiency from blood loss.