The advice about a 3 months window period applies only to the
HIV antibody tests, not the duo
test (for both
HIV antibody and p24 antigen), which is definitive at 4 weeks. Below is a link to a thread that discusses window periods, and the reasons that official advice remains 3 months despite scientific evidence that earlier testing is conclusive.
http://www.medhelp.org/postst/show/1704700
The oral swab self test is pretty much fool proof. That result also is 100% reliable.