What Causes Severe Headache?

Hello, if I have had sex with a girl with out a condom, and this girl has had sexual intercourse (penis up the vagina) 3 times with different people and they all wore condoms, and they were clean and she is clean so they say, what is the chance that I have anything? P.s am starting to get really bad headaches and sometimes feel sick, and I had sex with her 3 days ago? Is it normal? Or is it because am so paranoid its getting to my head so I have a headache! Am very worried.