I will give you my opinion.
It is the most probably you didn't get any H. Pylori from the HPI.
H. pylori is a bacteria that don't give symptoms from night to day. In fact, most people who get H. Pylori have it since the the first years of life without any gastrointestinal symptoms. If I were you, I won't take any Antibiotic until a test shows H. Pylori. H. Pylori ( the bacteria itself ) isn't found in stool but the antibody against it. Antibodies in blood have memory so, the only relieable test to detect H. Pylori is an antigen in stool or an intestinal biopsy. The breath test can give false information. Even if you are positive for H. Pylori, I put all my money it wasn't adquired by the HPI. To develop a gastritis caused by H. Pylori you need years with it. Nobody get symptoms from adquiring H. Pylori in only a few days. Also, I see no way to adquire H. Pylori from stool because it isn't normally present in it. Another thing is your donor was H. Pylori negative.
There isn't proof the H. Pylori is present in stool because studies aren't conclusives. This article talks about it. http://qjmed.oxfordjournals.org/content/92/7/361.full