Suggest Treatment For Groin Pain

Hi, I have recently started to get pain in my right groin. The pain only exists when I walk and usually starts after 5-10 minutes of walking. The pain does not exist if I run - only when I walk and sometimes when I am lying down. I exercise regularly, gym, running, golf and soccer. I am male 49 years old. I have been diagnosed previously with Ankylosing Spondylitis but do not have any long term effects and have not had a flare up for over 10 years. Just wondering how a groin strain can hurt when walking but not when running? Can you help please. Thanks....Mark