Thanks for your question, sorry to hear about your concerns. Obviously, there is a possibility that you could be pregnant. While the likelihood of this may be low, no birth control
is 100% effective, even if they may be 100% effective in theory. While tubal ligation is an excellent method of birth control, there are times that it does not work for some people (although these rates are very low, and compare favorably to the best hormonal birth control pills, or oral contraceptives as they are also known). For that reason, it is important to speak with your doctor
about your question. While a pregnancy test, available over the counter, may help to allay your fears by saying that you are not pregnant, it will not necessarily explain why your menstrual cycle is irregular. This is the question that does need to be answered, as it may point to other problems in your health. These problems may be as simple as stress, or may be much more serious, but your doctor will be able to help you understand what measures need to be taken to help you feel better. Please speak with your doctor about this question.