Hello, There is some risk of unprotected oral sex, but the risk is less than that from unprotected anal or vaginal sex. However oral sex carries a lower risk of HIV transmission but the risk is not zero. So to be sure if You are HIV positive/negative You should have an HIV test. Please note that from 2 weeks to 6 months HIV antibodies may not be detectable - it is called a seroconversion so You should have an HIV test within 3 months of Your possible exposure to HIV and than You should be retested 3 months after that first test. If both tests will be negative it means that You are not HIV infected. 11 days after unprotected sex is to early to have an HIV test. You have also written about pain on the back of Your head. Headache may occur but the most common symptom (within 2-4 weeks after HIV infection) is fever, than others like swollen glands, sore throat, rash, muscle and joint aches and pains. The most common HIV test is Antibody Test like Enzyme immunoassay (EIA). Another is Antigen Test and it is used to diagnose HIV infection earlier - from 1-3 weeks after HIV infection. And the third one is PCR Test to diagnose HIV infection from 2-3 weeks after exposure. In my opinion You have small chance to be HIV infected but there is still a need to have a HIV test. If You choose EIA test remember that first test should be done within 3 months after exposure. Hope I have answered your question. If you have any further questions I will be happy to help.