Late seroconversion is an old myth. Docs can't diagnose hiv from symptoms so no one here pays attention to whatever symptoms people post here that they think they have and you shouldn't either.
"My ex girlfriend is arguably saying she had a test " Arguably? Not sure what you meant.
A duo test is conclusive after 4 weeks and any other after 12. It s best if both people test before starting an unprotected sex relationship - do that if there is a next time. If she had tested past the window of her last unprotected with her ex, then you should forget about hiv. If not then ask her to test now.
You are plainly being told to take a test. Worrying about symptoms and GBS is not helpful to you. HIV is never diagnosed through symptoms or guessing that something going on with you is related to HIV. That's not how it works. It is ONLY diagnosed by a test. If it has been a month, that means you can take a Duo 4th generation test which is conclusive from day 28 on. However, the things to keep in mind is that a single vaginal sex exposure is extremely LOW risk, around 1 percent at best. It also wasn't a high risk person as your ex girlfriend. So, the odds say you will most certainly be negative. Quit analyzing symptoms and just take a test.
The test guidelines exist because of scientific principles, so if you can't get access to a duo, you will be wasting your time testing early with a different one. Try not to worry while you wait for 12 weeks and avoid googling because there is nothing there that can provide any answer for your status.
You only have 2 options. Get a duo or wait for 12 weeks for any test. Best to stop googling cold turkey and avoid thinking about it until then because nothing you read or think will affect the test.