"why do they do. This?" How could we possiblily know why your Dr would advise this? Next time make take her some proof that 3 months is the conclusive window period.
"Would it be a waste to test again?" I think you know this answer.
You tested negative at 6 months with a reliable test, beyond the standard 3 months window period.
Your negative test was done at a time even the rare people would have tested positive if they were truly infected.
You don't have hiv!
May God bless
Thanks for your answers..i appreciate it! Its just so unnerving that not everyone is checking up on the standards and instilling fear in people..