What Causes Spasms In The Lower Abdomen Every 15 Minutes?

Hi, I am a 54 year old male that is in great physical shape. I look 35 and am as fit as one. In the last seven days or so, I have experienced spasms in my lower abdomen. They do not give me pain but very obnoxious! It almost feels as though it is above around my bladder. Does this situation sound familiar? I do lot s of pull ups, crunches, planks and curls. I have done this consistently for many years. These spasms happen about every 15 to 20 minutes. Do you have any suggestions? I would be grateful!