What Causes Passing Of Black Stools?

My name is John. On or about 12/22/2014 while having a bowel movement I noticed at the completion of the session something I never saw in my 69 years. I looked at the stools in the toilet and black stools. I was concerned so much so that after i cleaned myself I proceeded to my computer and accessed maoclinic .com. I have a sleeping problem of which for many years I was taking Advil PM. I read the label on the bottle and saw diphenhydramine and ibuprofen and the affects it can have on persons over the age of 60. I immediately discarded the Advil and three days later something interesting occurred. The black stools went away and when I wiped using the tissue paper there was no more evidence of the black colored stools. As of 01/15/2015 I no longer see black stools but normal brown color stools that I have been seeing all of my 69 years. After seeing the black stools back on 12/22/2014 I immediately made an oppointment with my doctor on 12/26/2014. I told him exactly what I have written above. He recommended that I should consider undergoing a colonoscopy. My last colon exam was back in 2012. I suggested to him do you think doctor that I should see a urologist for a rectal exam. Gentleman can someone assist me with an answer to my problem.