It is always difficult to be able to diagnoseyour son's skin rash without being able to see him, but from your description he appears to have had a rash called impetigo recently. This is caused by a bacterial infection, usually by strep or staph.This is why the doctor gave him an antibiotic. The new rash is puzzling especially as it leaves a dark scar. It is possible that he has a recurrence of the impetigo, but this does not usually cause a dark scar.A tick bite can leave a dark scab but then he would not have so many sores. It would be best to take your son to be seen by a dermatologist.
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