I am almost certain that it is not a hernia. My brother in law had one and the pain that he described was much different than this.
There are different types of hernias and they can vary from minor to major. If there is a hernia though you should be able to feel a lump in the area.
The lack of fever would likely rule out infection.
Another possibility is an aortic aneurysm. These often do not pose symptoms though. If they do the pain will feel "deep" and may radiate through to the back. Sometimes the person can also feel their pulse in the area. If you do not feel a lump there and do not think it is a hernia it would be a good idea to have it checked out. Not many things will cause pain directly in the center of the abdomen. And if it is an aneurysm this can be quite dangerous so it would be best to have it checked out.
My stools are loose. Not diarrhea or watery loose but thin, stringy loose. I'm not certain if there is blood in them or not. Its a consistent color, more brownish but maybe a hint of blood. Though it may be just a different color because of the general change in bowel movements.
After 2 days of fiber the stools solidified a bit more but still are a bit more stringy and smooth.
If something was going on in the intestines there still should not be centralized pain so this is not likely related.