you didn't mention your age, these type of menstrual irregularities can be seen in perimenopausal age group because of hormonal
in reproductive age group also different kind of problems can affect hypothalamo-pituitary-ovarian axis leading to menstrual irregularities, as you undergone tubectomy the chance of pregnancy
is very less though cannot be completely eliminated,
so you consult gynecologist, undergo physical examination and ultrasound
to find out the possible cause and treatment can be taken accordingly.