點解胃痛時,連背部也會痛?

不只 胃痛時,背部會痛,
所有人體內臟 有問題, 都會 連背部也會痛.
尤其是 胆石 and 腎石.

點解胃痛時,連背部也會痛: is called "Referred Pain" in medical terms, and you can look it up if you want more info. Basically what it means is that the nerve supply to various internal organs is often common in origin, eg nerves to the 背部 also supple the 胃部. The pain is also poorly localized. This is in contrast to nerve supply to the skin, in which when someone pokes you with a needle, you know more or less exactly where they have poked you!
This is the difference between Visceral Pain and Somatic Pain, Visceral pain: internal organs, Somatic: body eg skin

胃痛: typically has pain over the Epigastric region(higher than the umbilicus and in the middle). It is dull in nature, related to meals, relieved by antacids. The pain is common to radiate to the back.
You should also beware of other features eg Black Stool(ie black shit), which can suggest upper gastrointestinal bleeding. It would require further investigation by a medical practitioner.

Epigastric pain with radiation to the back can also be caused by: Pancreatitis, Gall stone or biliary tract diseases, abdominal aortic aneurysm or even ischemic heart disease. (in female: menstruation also)

Well in conclusion, if the problem worsens or there are other worrying features eg weight loss, loss of appetite, vomiting (coffee ground colour vomitus) or even black stool, go see your doctor for further investigations