Your syphilis test is conclusive.
At 6 weeks, your herpes IgG test is probably 70% accurate. If you haven't had any symptoms, I would take it and run. If you test again, there is a decent chance of a false positive, and unwinding that takes weeks and a lot of money, not to mention stress and anxiety.
If you've had symptoms, my advice might change. Also, did you use a condom?