I Am 40. First Time Ever I Have Crossed 8

I am 40. First time ever I have crossed 8 days above my regular cycle of 25Day periods. I performed urine (not in the morning) home pregnancy test, which was negative. My doc suggested 5 day course of deviry 10mg and wait for a week after the course for bleeding to occur. Am I following right steps? Am afraid about possibility of being pregnant. Plz suggest.