Welcome to e health forum.
HIV symptoms can be very confusing, and many other conditions can be mistaken for HIV. Hence HIV is not diagnosed based on signs or symptoms. It is diagnosed based on serology tests detecting HIV antigens and antibodies in the blood.
Chances of having a confirmed HIV infection, just by a single sexual encounter is very less.
Weight loss in your case, is most likely due to stress and anxiety. The enlarged tonsils are probably due to bacterial infection, and may need proper treatment with antibiotics and other supportive medications. Hence you should consult a doctor for a proper examination and help.
In case, of doubt, you should get over your fears and get tested for HIV. This will clear all your anxiety and stress and help you move on with your life.