2 serious questions on herpes. Need a clear understanding

This might sound stupid but never been dx w herpes and the more I read up on it. I read that normally your dr don’t screen you for herpes unless you are showing signs or ask to be screen bc you only can treat the symptoms. My questions are:

1. When I had present w symptoms why they didn’t do a culture on it? Wouldn’t that be more accurate?

2. Is is possible to have positive IgG and than months down the line have a nagativd IgG

The reason why I ask these questions because the more articles I read up on it. You can be living w herpes and not have one symptoms of your life time. It’s very hard to tell whom you got it from if your first time been dx w it shows a positive IgG and negative IgM.