When Im standing relatively still (working on checkout) for a couple of hrs I get a constant pain in my left side. It gets worse as time progresses until I have to sit or lie down. I also get the same pain if Im walking through stores slowly shopping. It clears up after I have been sitting for a while, I dont get pain when I walk fast for long distances ( I walk daily so Im quite fit) or when I do physical workouts in gym. This started about 3 yrs ago and is a constant problem if I have a big shop to do that takes some time