An IgG now would give you a baseline for HSV 1 and 2, but yes, way too early to get a reliable answer and yes, the IgM is poor and often gives false positives.
The symptoms that you are experiencing could be due only to the trauma of anal sex but I would recommend that in this week coming up, you get a full STI screen for things like gonorrhea, chlamydia from the anus.
You can do a fairly reliable IGG test in 6 weeks – not perfect but OK
Terri