Hello!
Sorry your son has been sick. It IS possible that he could still have strep throat as an infection. Some people never actually completely eliminate the bacteria (called Group A Strep) from their throats, even with antibiotics. Some of the bacteria are resistant to the antibiotics used, and your son may need a different antibiotic that would kill the bacteria your son has specifically in his throat.
He may not have completely been cured of the infection, which is why he could still have it.
Another possibility is that he simply has a virus infection, not a bacteria. 90% of sore throats in children are actually caused by viruses, so do NOT need antibiotic therapy. It may just be bad luck that he's sick again, and if he goes to day care, he may continue to get infected from the other kids.
The only way to know for sure would be to bring him back to the doctor, and have the doctor swab his throat for a culture to see 1) if he has a strep infection or not and 2) if he does have strep, if it's resistant to the regular antibiotics.
Good luck. Let me know if you have more questions.
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