For eight years, Jessica Terry suffered from stomach pain so horrible, it brought her to her knees. The pain, along with diarrhea, vomiting and fever, made her so sick, she lost weight and often had to miss school.

During a science class, Jessica Terry, 18, discovered a tell-tale granuloma in her own pathology slide.

Her doctors, no matter how hard they tried, couldn't figure out the cause of Jessica's abdominal distress.

Then one day in January, Terry, 18, figured it out on her own.

In her Advanced Placement high school science class, she was looking under the microscope at slides of her own intestinal tissue -- slides her pathologist had said were completely normal -- and spotted an area of inflamed tissue called a granuloma, a clear indication that she had Crohn's disease.

"It's weird I had to solve my own medical problem," Terry told CNN affiliate KOMO in Seattle, Washington. "There were just no answers anywhere. ... I was always sick."

Terry, who graduated from Eastside Catholic School in Sammamish, Washington, this month, is now being treated for Crohn's, says her science teacher, MaryMargaret Welch.

"She was pretty excited about finding the granuloma," Welch said. "She said, 'Ms. Welch! Ms. Welch! Come over here. I think I've got something!' "

Welch, who has taught the Biomedical Problems class at Eastside for 17 years, immediately went on the Internet to see whether Terry had indeed spotted a granuloma.

"I said, 'Jeez, it certainly looks like one to me,' " Welch remembered. "I snapped a picture of it on the microscope and e-mailed it to the pathologist. Within 24 hours, he sent back an e-mail saying yes, this is a granuloma." Watch Terry describe her experience »

Although Terry was relieved to finally get a diagnosis, it was also tough for her to hear that she has such a serious disease.

There are treatments, but there is no cure for Crohn's, a condition in which the digestive tract becomes inflamed. It can lead to ulcers, malnutrition and other health problems.

"As I get older, the disease can get worse," Terry told KOMO.

Crohn's disease is often misdiagnosed or diagnosed very late, says Dr. Corey Siegel, director of the Inflammatory Bowel Disease Center at Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire.

"Granulomas are oftentimes very hard to find and not always even present at all," Siegel said. "I commend Jessica for her meticulous work."

Pathologists also sometimes miss important findings for other diseases, says Dr. Mark Graber, chief of the medical service at the Northport VA Medical Center in New York.

"This story carries a valuable lesson about how errors are found. It's very often by 'fresh eyes,' just like in Jessica's case," he said. "Some specialty centers, recognizing the reality of perceptual error and the power of a second independent reading, are now requiring second reviews on certain types of smears and pathology specimens."

Welch credits Terry's "fresh eyes" but also local pathologists who volunteered to train her and her classmates on how to view specimens under the microscope.

"We've been lucky to have that partnership. It allowed Jessica to think of herself as a scientist," she said. "The class empowered Jessica to think of herself as being a partner in her own health care."

As for Terry's future, she'll start nursing school in the fall. She's written a book for children about Crohn's disease, which she hopes to have published. In the meantime, she's grateful for her science class and for the pathologist for giving her her slides.

"This has been the highlight of my high school career, for sure," Terry told the Sammamish Reporter newspaper. "It's been amazing."

CNN's Jennifer Pifer Bixler and Sabriya Rice contributed to this report.

All About Crohn's Disease • High School Education