What leads to constipation and late period, together?

I would consider: pregnancy test at least 1 week after your late period, if your period never came. If negative, test again in 1 week. The longer you wait the more sensitive the pregnancy test becomes. If you start having a regular period then it's unlikely that you are pregnant. Otherwise you may be pregnant until proven otherwise.

Take home pregnancy: test to know. Reasons for missed /late periods: low body weight, obesity, marked weight gain or loss, over-exercise such as in endurance athletes, breast-feeding, stress, illness, eating disorders (bulimia or anorexia), travel, hormone irregularities, drug use, medications (i.e., birth control) or med problem (polycystic ovary syndrome or Asherman’s syndrome. #1 reason is pregnancy.