Appendicitis is not always easy to diagnose. Describe how the symptoms came on.
When my ex got sick one day while I was at work, he called me. He described abdominal pain that sounded like it could be gas or early appendicitis. I told him to take Gas-Ex and lie down. When I got home, he still had the pain, even lying down. I pressed on his abdomen and he had more pain. Didn't really know what I was doing, but just gently pressed around and he moaned. The pain had moved from his umbilicus to more in the right lower quadrant. Despite his claim that it was only 4/10 pain level, I told him to take a quick shower and then we were going to the ER. I called my surgeon to meet us there. He was a little stunned because he'd just taken my gallbladder out 6 weeks before. We first saw the ER doctor. I did not tell her what I thought it was; just said abdominal pain. She checked his white count and said it was too high to be appendicitis. As soon as she left the bedside, I told my ex I still thought it was appendicitis. The surgeon got there and heard the story, saw the white count, and examined him. He said it was gangrenous appendicitis and started an IV. Then after 6 hours or something he took out his appendix.
So yeah, it can be confusing sometimes. The thing they most often confuse it with is diverticulitis. That can be even worse than appendicitis though.
According to WebMD diagnosing appendicitis can be tricky:
"Symptoms of appendicitis are frequently vague or extremely similar to other ailments, including gallbladder problems, bladder or urinary tract infection, Crohn's disease, gastritis, intestinal infection, and ovary problems.
The following tests are usually used to make the diagnosis.
Abdominal exam to detect inflammation
Urine test to rule out a urinary tract infection
Blood test to see if your body is fighting infection
CT scans and/or ultrasound"
Welcome to the gastroenterology community! A CT scan is the best test for diagnosing an appendicitis. If you have had a CT scan with contrast of your abdomen and it came back negative, then you can rule out appendicitis.