After a week, what could cause sore throat, headache or a lower abdomen pain after unsafe oral sex?

Many infections: You could just have a cold but any sexually transmitted disease that can be passed by vaginal or anal penetration can be passed through oral sex as well. It is a little more difficult but i would not bet my life on it. See a doctor or your std clinic. Syphilis, herpes, hiv, hpv, gonorrhea, chlamydia, chancroid, and lymphogranuloma venereum.