Hello, Irregular menstrual bleeding can be caused by many causes and pregnancy is one of the possible causes as well. Even though you have had tubal ligation it is safer to just have a pregnancy test and rule it out. If the pregnancy test comes out negative then you will need to see a doctor and have a gynecological exam. The doctor might need to take a pap smear if you have not had one in the last year or two and he might also ask for transvaginal ultrasound to check for uterine inner layer (the endometrium thickness) and also if there is any masses. Most of the times all tests come out normal and then hormonal causes are suspected and follow up in time is the best management. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Antoneta Zotaj General & Family Physician