Is there any antibiotics that are least likely to cause allergy or stomach upset? I can't find one that doesn't cause a problem. Thanks.

Stomach upset is one thing - a true allergy is another. Stomach upset can behelped by taking the meds with food (bread and cheese work well). A true allergy cannot be overcome.

many antibiotics cause stomach discomfort.. that's one of the unfortunate side-effects. Like titchou said, allergies are a different story and also are different form person to person. Something I'm allergic to, you might not be and vive-versa.