Bowel problem.

I am 68 years young male and have had diabetes for ten years. My problem started about a year ago whereby I have to strain something awful when I have to have a bowel movement. I'm not constipated (this is embarrassing) but I manage to relieve myself about once a week compared to three or four times a week before. I have to take insulin and Tolinaze daily. The straining is extremely painful with regards to the pressure on my body. Can anyone advise me what I should do to rid myself of this infliction. I've tried laxatives without success. I'm afraid of having a heart attack during one of these straining sessions. I've been told it is the result of having diabetes but I know of no-one else with the same problem. Please e-mail me at STORYLAD@AOL.COM with any suggestions. Thank you.
Jim