Every Winter I Get An Constant Upset Stomach. I Am

Every winter I get an constant upset stomach. I am a 71 years old male, and have experienced this for 5 years in a row. The first year, I went to my doctor who sent me to a specialist. The doctor did extensive testing on me, which concluded with a breathing test that lasted several hours. The prognosis was a stomach infection that was treated with medication the first and second year that I had the symptoms. The third and fourth year, I self -treated with "Culturalle", an over the counter drug that did as well as the medication I had taken the previous 2 years.
Please help me find an answer as to why this happens, and why?, only the winter months in Buffalo, NY?
Thanking you in advance for advice you can give me!
Larry Richardson
716 649-8559