What can be the cause of having a 13 day late menstruation cycle.I took a PT test and it was negative.?

If you are stressed out for any reason (i.e. new job, divorce, move), that can cause you to miss a period or for your period to be late.

Also, if you have had any rapid weight gain or loss recently.

Sometimes medical conditions can cause a late period. I had a friend who had a benign tumor on her hypothalamus gland. It caused her body to produce prolactin, normally produced when a woman is pregnant or nursing. So in a way, the tumor "tricked" her body into thinking it was pregnant, so her periods stopped. Other medical conditions that could cause a period to be late could be ovarian or uterine cysts.

You may want to talk to your doctor if it doesn't come within the next week or so. Best wishes to you.

stress, a new exercise routine. both can be causes of late or even skipped periods

If i totally mess up my birth control pills one month...i get the longest period in the world!!!

You could be under stress.