Having just stood in for an appendicectomy today, I feel I can comment on this disease.
The classical picture of appendicitis is one where a vague, colicky epigastric pain turns into a sharp pain in the right iliac fossa. The right iliac fossa pain is moderate to severe, often unremitting and is worsened by movement. Anorexia is another classical feature whilst fever may or may not be present.
If the pain has progressed to being very severe and is now located all over the abdomen, it means that the appendix has perforated and there is peritonitis in the patient's belly.
An important lesson I learnt from the surgeon whilst holding retractors for her on the operating table was that having diarrhea or blood/white cells in the urine does not exclude appendicitis. Appendicitis can sometimes cause diarrhea through irritation of the nearby ileum and similarly can cause irritation to the ureter if it passes next to the appendix (the location of the appendix is variable).