Hi, Irregularity in menstrual cycles can occur due to many causes, but according to your history the possibilities are ectopic pregnancy, the condition when the gestational sac develops outside the uterus, usually in the fallopian tube or in ovary. This can be seen in people who have undergone tubal ligation also. As this is an emergency condition, it is better to consult your gynecologist immediately and undergo a blood test for pregnancy and ultrasound with this work up the possibility of ectopic pregnancy can be identified and treatment can be planned accordingly. In the absence of ectopic pregnancy, the other possible cause is irregular periods due to reproductive hormonal imbalance and pain due to to possible adhesions due to previous surgery. In this case the cause of the irregular period should be evaluated and antispasmodics can help in relieving the pain. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sree Gouri S. R., OBGYN