How Long Can a Stomach Virus Linger?

Two weeks ago my 9 year old son said he had a stomach ache, and he thought that he was hungry. He ate some crackers, had a few sips of ginger ale, and he seemed completely fine. However, an hour later, he made two back to back trips to the bathroom. He had more of a loose stool than actual diarrhea. He went once more that afternoon, twice the next morning, and did not go at all the next day. He never had a fever or lost his appetite or energy level. In the meantime, my husband started having really bad diarrhea, fever, chills, loss of appetite, etc. My husband went to the doctor, who thought it was viral, and said there was a very bad bug going around that has even put some patients in the hospital. The next morning my son said his stomach hurt again, and went to the bathroom three times in a row. His stool had quite a bit of mucus. We went to the pediatrician who also thought it was viral. I collected stool samples. They tested for c-diff (he had strep three times in March), salmonella, rotovirus, and some other viruses/bacteria. They didn't test for parasites but I don't think that's likely. Everything was negative. My son seems to be slowly improving. This past week most days he was back to his normal bathroom routine, although sometimes I saw mucus in the stool. This morning, however, he went to the bathroom four times. The pediatrician did not seem concerned when I called- he said mucus is not unusual during a stomach bug. Also, my son just started having really bad nasal allergies and he is taking Claritin for the first time. I wonder if the Claritin could have caused the frequent trips to the bathroom this morning since it is a new medication and he is not used to it. Also, could the ton of nasal congestion he has show up in the stool? I didn't ask the doctor these questions, but I think we will be back there next week if this continues. My son seems fine and has a huge appetite. He has never had any food allergies, but I suppose a referral for an allergist would also be a possible next step. Have any of your children had loose or frequent stools that lasted for a while at the end of a stomach bug?