Lack of menstruation is the first, albeit, insecure sign of pregnancy. Other conditions that can also cause lack of menstruation (a functional ovarian cyst, hypogonadism, PCOS etc.). A negative pregnancy test is a fairly secure sign that you are not pregnant. You may consider the bleeding you experienced on the 4th of February to be a mesntrual period.
Those stories, you’ve heard, about “pregnant women with regular periods and negative pregnancy tests” are complete nonsense.