What Causes Loose Stools, Gastritis And Nausea?

Went out to eat on Saturday to a buffet style dinner. I noticed on Sunday I was a little gassy, I took some antacid. Monday during the day I was not feeling very well in the stomach lower and upper. I started going to the bathroom, passed lots of gas, loose bowels, gas from the mouth…lots. This morning I vomited with loose bowel and nausea. My stomach pains, a deep pain, feel like going to the bathroom. A squeezing pain and lots of noise and activity. This is the second day, but symptoms really started this morning. I feel very tired with pain across by back.