What Cause Blood Appears In Stool?

I am wondering if blood in the stool could be caused by stress. The blood is bright red and sometimes clotted (the clots are somewhat darker than the rest of the blood). I have had this before, about once a year. But lately it is increasing in frequency to where it is almost monthly. In the past it has been spotty, but over the past weekend it has lasted for over 24 hours, stopped for a couple of days, and then began again. I am under a great deal of stress at work, including a very stressful event last week. I have asked a doctor in the past about this and was told not to worry, but with the frequency increasing I am wondering if I should be more concerned. Thank you.