I Am 65 Years Old And I Have Started To

I am 65 years old and I have started to exercise 3 times a week and I am experiencing a change in my bowel movements which are like small firm balls not pellets about an inch in diameter that often cluster into rather large masses not easily discharged. There is no blood and I consume quite a bit of fiber in my diet and am well hydrated. Should I be concerned? Why is this happening?