Well, I'm not a doctor but I will say that you seem to have made some big changes in your diet since the first of the year. Big changes can be hard on our systems and eating things like onion rings or french fries which are deep fried, probably in the same fat where meat is deep fried seems like a logical way to get a stomach ache and diarrhea.
Unless you are having chronic diarrhea, weight loss, blood in your stool, daily bloating and gas, or other severe symptoms I wouldn't think this is anything more than making poor food choices among healthier food choices. Try cutting out the greasy food and see how you feel.
But, as always, if you are truly concerned then do make an appt. with your doctor to discuss your symptoms.
Cheers,
Elizabeth