55 Day no period

Katie

I am 42 years old, & have been having sciatic pain sense first week of Nov. That was also the end of my last period. I have not had a period sense. Doctors have proscribed pain meds & taken X-rays of my lower back & found nothing. I took a home pregnancy test about a month ago. Turned out to be negative. I also have my tubes tied for 16 years. Question: is there any reason why my period is this late. It never has been my whole life unless I was pregnant.