Dear At Wits End
If you feel that you are this ill then you may want to see your physician.
Have you ever been told by a Doctor that your type of anxiety may be health anxiety. You are assuming the worse regarding your symptoms and researching all the really bad things it could be. The more you read the more anxious you get and pretty soon your caught up in a vicious circle.
Peritonitis is usually caused by an infection spreading from an infected organ in the abdominal cavity. Common sources are perforations of the stomach, intestine, gallbladder, or appendix. Infection can also spread to the peritoneum from other parts of the body through the blood. The peritoneum (the membrane that lines the abdominal cavity and organs) is remarkably resistant to infection. Unless contamination continues, peritonitis does not progress, and the peritoneum tends to heal with treatment
Reference: Merck Manual, 2nd Home Addition
If you read every article on this topic you will find all kinds of scary causes. So please consult a physician if you need as I am not an expert and I do not diagnosis. :)
Please take care as I am very concerned about you. (((HUGS))))