Did you get a different kind of test for syphilis? It should say RPR or VDRL, or FTA-ABS, but not IgG.
I also wouldn't worry about either that much, but if you feel the need to test, make sure it's the correct tests. https://www.webmd.com/sexual-conditions/syphilis-diagnosis
And yes, the IgM is unreliable for herpes.
By the way the igm test for herpes is unreliable
90% of people that are positive for syphilis will show antibodies at 3weeks I would believe your test and move on
I would worry about herpes. And if all you had was oral there was little risk and no need to test