I’m not aware of problems with false negatives for the IgM test, no, but because there are problems with the test in general, I can’t honestly say how reliable it is. But as you seem to know, the reliable test is the type specific IgG. The grouped IgG as you describe is not helpful unless completely negative. Even then as with the IgM, I’m not sure how reliable it is.
Five days of acyclovir will not interfere with the IgG test, no. You can certainly test as you go along at 8.5 and 12 weeks but the most reliable test will be at 16 weeks. So I’m a little confused here – do you have a baseline IgG test at all? If not, and it turns out positive, you will not be able to know if you just got infected or have been infected for years, right?
Xanex will not interfere with testing no.
May I ask what country you are living in?