I am 25 years male had a sexual exposure after 1.5 years and 1.7 years I tested with hiv duo combo and std panel all the tests were negative. But I am having white tongue and some people saying that after more than year body's defense mechanism stops at that time hiv can't be detected or if your immune system is weakened hiv cannot be detected need to cd4 count they are saying. Is it required to do other tests or not?