I am a 38 year old female , im not pregnant and i have not had a menstrual cycle in almost a year. im really scared, i plan to get it checked out this week but does any doctor know the most common reason for this to occur in women my age?

Many possible causes: There are many possible causes of your condition which is called amenorrhea. Among these causes are nutritional deficiencies, birth control pills, stress, low body weight, eating disorders, excessive exercise, excessive weight gain, psychiatric drugs, other mediations, polycystic ovary syndrome & thyroid problems. You're right to get examined soon, so please try to relax. I wish you well!