Welcome to the forum. Thanks for your question.
My first advice is to comment on the fact that you had unprotected sex with a partner you don't know well. I hope that won't happen again. Please get into the condom habit! Still, the chances your partner had HIV or that you were infected are very, very low.
I think your doctor doesn't understand HIV testing, especially with p24 antigen, or that you misunderstood something.
The "4th generation" HIV blood test (also called "combo" or "duo" test) checks for both HIV antibody and p24 antigen. With this test, a negative result at 4 weeks or more after the last possible exposure is 100% reliable. Although many agencies continue to recommend that a final antibody-only test be done at 3 months, it really isn't necessary. For more information, see the link below.
http://www.medhelp.org/posts/HIV---Prevention/p24-test/show/1704700
Also, test results override all other considerations, including symptoms and exposure history. Even if you knew your partner had HIV (probably she did not) and even if your sore throat were typical for HIV (it is not), your negative test shows for sure you were not infected. You not be at all worried.
I hope this has helped. Best wishes-- HHH, MD