Hello, this forum is US based and we must follow CDC's guidelines, according to them any HIV test is conclusive if taken 12 weeks after an exposure, but you can take them before that, 3rd gen will give you an excellent indicator about your status around 6 - 8 weeks after exposure and 4th gen 4 - 6 weeks after exposure. A result given in those times is very unlike to change, but only a doctor, based on your risk level and his experience could advice you to skip the confirmatory test after 12 weeks post exposure.
Hope this helps.
Should I have another test?