I Have Had Some Rectal Bleeding That Started About A

I have had some rectal bleeding that started about a year ago. At first it was just streaks in my stool. Then it progressed to blood in the bowl, and bright red bllod on toilet paper, but not all the time. I went to the doctor, who said I had a hemorrhoid and told me to use Preparation H. I did and it cleared up for a while, but now it's back. I am having a lot more flatulance and way more bowel movements than usual. The stools themselves are of normal colour and texture. This doesn't happen every day or all the time, but seems to be related to when I drink a lot of dieta cola. Could this be the cause?