Im afraid there is no easy answer to explain your recent problem.
Surely a viral illness can cause cramping and diarrhea, with both made worse by a meal heavy in fat. These symptoms can persist for a while even after the virus is out of your system. But I have no information about other symptoms, such as fever, nausea, and fatigue that would help in making this diagnosis.
Cramping and intermittent diarrhea are signs of irritable bowel syndrome (IBS), which is often aggravated by stress. But it would be unusual for IBS to show up for the first time at this stage of your life. Plus, people with IBS dont usually have nighttime symptoms. In fact, one useful clue for doctors that it is IBS is that sufferers have peaceful sleep despite a day wracked by cramping and diarrhea.
The fact that your pain is made worse by a fatty meal brings makes me think of a gallbladder attack. Typically, these attacks happen after a dinner rich in fat. Youd likely feel intense pain in your upper abdomen. And the pain generally lasts for hours, and it sometimes spreads to the back and right shoulder. Also, diarrhea is not a symptom of a gallbladder attack. So your description makes this problem less likely.
Another possibility is microscopic colitis. This is a disorder that is being found much more often than in the past as a cause of diarrhea in women your age.
Your best bet is a visit to your doctor. A more complete history and a physical exam may give some clues. Your doctor may also order an abdominal ultrasound exam to look for gallstones, as well as other tests.