@Zaf92,
When a doctor says an HIV test is negative, it means you don't have HIV.
When a doctor says the test is "very conclusive" it means that the chance that the test is wrong is very very small. You almost certainly don't have HIV. The doctor is telling you that the risk is so small that you should just stop worrying about it.
It is not exactly clear what it means when a doctor says "if you have symptoms, get tested". But given the fact that this doctor has told you you don't have HIV and that you should stop worrying about it, he may be just trying to get you to go away. You don't have a disease, be happy... and come back when you have a real problem.
If I were you, I would stop worrying about HIV which you don't have. There are plenty of other things to worry about, like Encephalitis or falling meteors.