Sorry to hear that Harley hasn't been feeling well. On young, otherwise healthy pets; it is common to have 'normal' physical examinations. Sucralfate is a good and very safe medication.
If you are looking for food options that are not 'home cooked' (I agree they can be a big commitment). There are several options. As far as OVER THE COUNTER: Science Diet makes a "Sensitive Stomach" formula that can help out in some types of food issues. Waltham and probably Pet Smart have similar formulas. Prescription diets can sometime help... there are several types, you will need to ask your vet.
If the problem does not resolve, I would take her back to your vet. Unfortunately sometimes the diagnostic path for these guys can be long.
Let us know how Harley does.