Max made a good suggestion, and certainly something easy to try.
Another possibility might be the Sulfites contained in the soups. I found the following information when researching food additives:
Sulfiting agents such as sulfur dioxide, sodium or potassium sulfite, bisulfite, and metabisulfite are used to preserve foods and sanitize containers for fermented beverages. Sulfites can be found in many foods, including baked goods, teas, condiments and relishes, processed seafood products, jams and jellies, dried fruit, fruit juices, canned and dehydrated vegetables, frozen and dehydrated potatoes, and soup mixes.
Sulfites may cause reactions such as chest tightness, hives, abdominal cramps, diarrhea, lowered blood pressure, light-headedness, weakness, and an elevated pulse rate. Sulfites also may trigger asthma attacks in sulfite-sensitive asthmatics.
Until recently, the highest levels of sulfites were found in restaurant salad bars. But in 1986, the Food and Drug Administration banned their use on fruits and vegetables intended to be sold or served raw because of the growing rate of sulfite reaction incidences. The FDA, in 1987, also ordered that packaged foods be labeled when they contain more than 10 parts per million of any sulfiting agent, so sulfite-sensitive individuals may identify which packaged foods they should avoid.
~~~~~~~~~~~~~~~~~~~~~
While it's not very easy to ask your hosts what ingredients they used to make the soup before accepting an invitation to dinner, you could try limiting your portion, and supplementing the soup with crackers or something that might help soak up whatever is hurting your tummy.
