Hi, as a blood donor, you must have had regular testing for infectious diseases like hepB, hiv, hepC, etc. When was last time you were screened for hbv and tested negative?
I hope the hbsag positive you got is just a false positive; anyhow you will get a clearer picture of your status from the blood test. Good luck!
Remember also when adults are infected with hbv, about 95% of them clear the infection by themselves within the acute phase of the disease, i.e. within 6 months.
"Blood" donor. Sorry for typo.