maybe an intestinal blockage. Is there discomfort? Are you regular with bowel movements? Is it sensitive when you press that lump? I would eat lots of fiber just in case it's something like that. Also avoid heavy meat eating or incorporate salads and other easy to digest foods when eating meat. Sounds like an intestinal issue but this is just a guess. When I've had symptoms like that, it's usually accompanied by a lot of discomfort...the above things have helped me. This is gross but if there is a dramatic change in the odor of your bowel movements or if they are very dark (sometimes a symptom of bleeding in there) you might want to call the doctor. Though you might feel ok now, taking care of it before the pain starts can save a lot of time and pain in the long run. Also noting what you eat before it occurs can help.
I have always had the same problem, would love to know what it is.
could be an anneryseum or hernia go to the DR