How long does strep throat last with anti-biotics (co-amoxiclav) i almost have it for 3 days and the pain is still there?

About that: The throat pain may not match the progress of the infection. Chloraseptic or Cepacol sprays can help w/pain, so can Cepacol or Sucrets lozenges.

Wait about 3 days: Streptococcus should respond to Augmentin (amoxicillin and clavulanate) within a week. However, if you do not get better, have a culture and sensitivity performed from a throat culture. That is the only scientific method to determine if the antibiotic will be successful.