 [ Symptoms ] if my son finished his treatment for strep and i was diagnosed the next day is he susceptible to it  my 2 year old son finished his amoxicillin treatment on tuesday and i was diagnosed with strep throat on wednesday how long does the amoxicillin stay in a persons system [ Disease ] hi u are suffering from sever gastroenteritis may be some food has caused infection inside your stomach take anti emetics and probiotics antacids will help cool down the heart burn consult a physician you may need to be started on antibiotics if things do not improve soon thanks