How conclusive are sti blood tests at 5 weeks post exposure?

Negative results at 5 weeks are not quite conclusive. Syphilis and HIV require 6 weeks, and some experts advise 3 months for syphilis. Herpes testing usually isn't recommended after a single exposure, but if done results are not conclusive until 3-4 months, and even then some infections are missed. If no symptoms, your 5 week results are highly reassuring, however.

Very good. HIV and syphilis may require a longer period require