Can sexually transmitted infections occur after oral sex?

Hello doctor,

I had a deep mouth kiss with a guy eight weeks before and then had oral sex with another guy, six weeks before. He also laid on my back and patted his tool but did not insert it into my anus. But his semen was dropped over my skin and outside the anus. I remember that I wiped it with tissue paper but I am scared that the semen would have transmitted into my anus on whipping it with tissue. Two weeks after that, I got body lice. I consulted a doctor and he gave me an ointment and he also suggested testing for syphilis, HIV (Human Immunodeficiency Virus) (fourth generation), and hepatitis. I exactly took the tests five weeks after the sex. All the results came negative and then I repeated the fourth generation test on the fourth and sixth weeks and still the results were negative. But still, I am scared because I see small acne-like spots coming over my face and it appeared on my thighs as well. Are my results conclusive? I am planning to take a viral load test tomorrow. Is it recommendable? Kindly help. I have done HIV combination test (p24 antigen, HIV1 antibody, and HIV2 antibody) and CMIA (Chemiluminence Microparticle Immuno Assay) serum test.