Q1.can a blood std test on itself only, with no other test,detect any std if vaginal,rectal and oral sex has happened? q2.i took cefaclor as part of a dental treatment during 5 days.two days after i did an std blood test?can this affect the outcome?

Blood testing cannot detect any STD at all until several weeks after exposure, and then specific tests need to be ordered (e.g. for HIV and syphilis); general testing (blood count etc) detects no STD. Most STDs require direct infection of exposed sites, like genital, rectal or throat swabs for gonorrhea and chlamydia. Cefaclor can make these tests unreliable, but not for blood tests.

Blood test alone is not enough to detect all STDs and taking Cefaclor does not change the blood test results for STDs.