How soon can blood test detect hiv, hepatitis b (surface antigen) and hepatitis c virus after unprotected sex? i feel burning sensation from 2nd day of exposure.

Different issues: The burning, I assume is on urinating, if so, you may have urethritis and depending on the type of bug involved, you may need antibiotic treatment. See a doctor for urine examination. Ask her/him about getting tested for HIV HepB and HepC to establish a baseline and repeat the tests at six months. The timeline for testing turn positive varies with the virus and the patient. Wish you good health.