I'm having dull lower left abdominal pain after I started running about an hour everyday. What could be the reasons. Male, 30, 150lbs?

Lower left pain. Most likely musculoskeletal issue. Could be a groin strain. Would stop running for awhile to see if it gets better. If so and stays away no issue. If pain comes back with exercise you should be checked for a groin hernia or even a "sports hernia" which is harder to diagnose and more controversial as far as treatment.