I concur with ANM and zell, this nurse gave you completely wrong information. You have already tested conclusively negative and your result won't change any further.
Stop reading about HIV online that's the core of the problem, there is a lot of good and bad information out there, some new and some outdated as well, I am not sure what did you read to get in to this fix.
Ideally, no one needs to test out beyond 3 months. 6 weeks is good for a conclusive with any standard antibody test. People with compromised immune system, which practically is, people who are on chemotherapy for cancer would be the only set of people who would have delayed detectable antibody production and subsequently need to test out at 3 months.
If you take recommendation from an experienced HIV specialist, they will only give you the aforementioned information.
Always use condoms correctly and consistently with people of unknown serostatus for vaginal / anal intercourse to stay away from HIV.
I will state again, you have tested negative conclusively and no further testing would be necessary. It is time to move on
The 4 gen was conclusive after 4 weeks. It is abnormal for you to test multiple times for the same disease so further testing indicates hiv phobia. You don't test 6 times for any other disease so your priorities are mixed up.
I have no idea why or even if the nurse said what you claim, however that is immaterial since the reality is 4 weeks is conclusive. Some sites are more conservative and use risks that have never manifested in real life or else they are outdated so you won't find consensus, however no one will say more than 3 months, so we can't argue with whatever you claim you heard somewhere.
Rest assured that your not infected because your multiple hiv test which are very very sensitive the duo test,have proven your hiv negative.