If 4th gen hiv tests for antigens of hiv they would spike up around 7 days. why do doctors on here recommend conclusive results at 6 weeks or 12? antigen levels go down after 1 month for antibodies to appear. 4 weeks should be conclusive for 4th gen?

Yes, the antigen-antibody (AgAb, 4th gen) HIV blood tests "should be" conclusive by 4 weeks, and that was the usual advice the first few years after these tests came into regular use. However, more recent data show that on rare occasions -- perhaps 1-2% of new HIV infections -- it can take up to 45 days, which is the current CDC recommendation. Advice often is rounded off to 6 weeks.