Thank you very much for your post and welcome to our forum.
Your negative Duo test done at 10 and a half weeks is final and fully conclusive. This confirms that you are HIV negative and that none of your symptoms are related to HIV sero-conversion. In fact your symptoms are not typical and do not correlate with HIV sero-conversion. The p24 antigen is already detectable after 14 days and can remain so up until 6 months. It becomes undetectable when the body has produced enough antibodies, which neutralise the specific antigen. One would never have a situation of not detecting the p24 antigen and the antibodies. At first one would have the antigen, after one would detect both, antigen and antibodies, and finally only antibodies. And antibodies are already detectable from 6 weeks onwards. Therefore I do not have any doubt in the relaibility of your negative result. HIV-2 is extremely rare and this is detectable with the antibodies of the Duo test, which at 10 and a half weeks would have been picked up.
Acute sero-conversion symptoms would all occur at the same time, between two and six weeks after the infection, not lasting longer than 14 days.
Your sexual encounter can be categorised as relatively low risk: unprotected sexual intercourse with a heterosexual man, I assume in Western Europe?
HIV-2 is extremely rare; we do not see any cases; most cases have been identified in West Africa or in people that have connections to this part of the world. The reason why it is so rare is because it is less aggressive than HIV-1, making less likely to infect. HIV-2 would normally only be missed if the Duo test is performed too early. ten and a hlaf weeks is certainly enough to have antibodies.
In summary, because of all the above, we can conclude that you are HIV negative without any doubt.