However, if you wait 3 weeks from the first time you notice the sore until you get a blood test, you could have made antibody during the 3 week period
, so it could get confusing. But if you have an antibody test right away when you notice the sore, and it is positive, then it is very likely an old infection.
If all you get is an antibody test, make sure it is an IgG test. If it is positive (at greater than 3.5), then you have old infection.