This year, I am 20 years old. These days, I often have symptoms of abdominal pain near the left belly button along with a little back pain, nausea in the middle of the night and pain in the early morning 5-10 minutes and then subsided. So the doctor told me the pain in the abdomen below the left navel with back pain indicates what disease?

Currently, I am in Japan. I have a dull pain in the abdomen below the right navel, usually at night for more than a week. I went to the doctor but the doctor said it was fine. What is the cause of lower right abdominal pain?