5. Ulcer
What it is: A sore on the stomach lining. Ten percent of the population will have one at some point in their lives.
What it feels like: Burning pain in your stomach that comes and goes but feels worse when you're hungry.
Fix it: If you're taking nonsteroidal drugs such as aspirin or ibuprofen, stop immediately, Peura says—these medications eat away at the stomach lining. See your doctor; you may need antibiotics to kill ulcer-causing bacteria, or even surgery.

6. Lactose Intolerance
What it is: Discomfort after consuming milk products due to a deficit in the enzyme that digests lactose, the sugar found in dairy products.
What if feels like: Nausea, cramps, bloating, gas, and/or diarrhea 30 minutes to two hours after eating or drinking foods containing lactose.
Fix it: Drink less milk, or have it with other foods to slow the digestion process. Try experimenting with an assortment of dairy products. Hard cheeses such as Swiss or cheddar have small amounts of lactose and generally don’t cause symptoms. Important note for the lactose intolerant: because dairy products are some of the most common sources of calcium, make sure you’re getting enough of that essential mineral elsewhere in your diet.