What causes sudden weight gain and gas followed by short pains in the abdominal area?

I am thinking that stress is the cause. I find the pills at the drug store called Gas X help

You do not say when this happens, but I am wondering if you are eating a large meal late at night? Try eating your larger meal in the afternoon and having a much lighter meal in the evening.Short frequent meals low in sugar and carbs tend to weigh you down. A high salt content in your food can also cause the retention of water in the body and lead to bloating. Try to go for walks after eating. Green tea in the morning speeds up the old body. If any of this works then great! If not, it could be something a little more major.

DO NOT DRINK GREEN TEA IF YOU ARE PREGNANT, at least not in large quantities, the EGCG compounds can affect folate levels in the body and the high caffeine content may be potntially harmful.

Another possible diagnosis is Celiac Disease, also known as Celiac Sprue or as gluten intolerance. It is a genetically inherited disease that can begin at birth, or can manifest later in life after experiencing some trauma (surgery, a car accident, child birth, etc.) It occurs when a protein found in wheat (gluten) cannot be properly absorbed by the digestive tract and triggers an autoimmune response, damaging the lining of the small intestine.

The symptoms of Celiac Disease are many and varied. Sudden weight gain, sudden weight loss, gas and abdominal pain, bloating, and nausea are common digestive issues associated with Celiac Disease. Other symptoms may be present, such as rheumatoid arthritis, fatigue, and difficulty concentrating. Celiac Disease is also commonly misdiagnosed as IBS (Irritable Bowel Syndrome), Crohn's Disease, or just "stress".

It is estimated that over 3 million people in the US have Celiac Disease, ranking it higher than Diabetes. The only cure for Celiac Disease is a lifelong diet devoid of gluten.