Misdiagnosis of Strep Throat, chronic stomach pain and lightheadness

Patient: Hello. My 12-year-old daughter has chronic stomach pain (she says level of 7), headache, some dizziness and lightheadness for several days now. She doesn’t have a fever, her throat is not sore, yet our doctor diagnosed her with Strep Throat (performed a strep test). She prescribed penicillian which my daughter has been taking for three days now, but she isn’t better and I would expect she would be somewhat by now. Her appetite is decreased, no vomitting, diarrhea or constipation and urine is clear. Could it be food poisoning of some kind? She has not been out of the U.S. What else might be wrong and would the next step be a blood test?