I would be pleased to answer your question .
following Antibiotic intake can occur after 15 days also . It is an effect which is called post antibiotic effect where the antibiotic remains in the blood and intestine vessels and causes changes in the natural flora.
You should take the Probiotic
for atleast 3 weeks .
You should also treat the gas which is a sign of gastritis
by some over the counter antiacidity .
Thanks and take care