Hello, doctors and epidemiologists around the world overwhelmingly agree that HIV is only transmitted by unprotected vaginal or anal penetrative sex, sharing needles or mother to child. Oral sex and masturbation are not considered risky activities, because there are no reports of people getting HIV by doing them.
You didn't even need to get tested for HIV in the first place, however unprotected oral sex might carry a small risk for other STDs, you could ask in the STD Forum if you wish.
4th gen will give you an excellent indicator about your status around 4 - 6 weeks after exposure. A result given in those times is extremely 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. But your risk was non existent.
If I were you, I'd believe the results and keep moving.
Hope this helps.
If you want to read more about the 12 weeks confirmatory test. I'd strongly recommend you to read the link I'll left here.
http://www.medhelp.org/posts/HIV---Prevention/what-is-the-window-period-for-hiv/show/1704700