I was wondering is it possible to have hiv and not be detected in the hiv ag/ab combo testing? is there a dormant phase? and for how long of dormancy?

It depends...: The HIV antibody-antigen combo or duo test ("4th generation" test) is always positive by 4 weeks. If it has been that long or more since your last possible exposure, it is not realistically possible that you have HIV. Most people with HIV remain outwardly healthy for years, so it seems dormant. But not really. The virus is active, damaging the immune system and leading toward death if not treated.