I’ll try to keep it short, 24 days ago I had oral sex give and receive with a trans, for 2 min, both of us didn’t cum, it was very brief and she/he said can’t cum due to hormones pills. 

I always have health anxiety so I’ve been stressed since then.

After 21 days I went to do full std test and all negative, until now 24 days since the exposure no obvious symptoms.

I’m mainly worried about syphilis and hsv2, h think my test results will change since I need to retest after 6 weeks, for how long should I look for sore-chances-blisters. 

Is my 3 weeks negative syphilis test reliable? 

Where should I mainly look for the sore-chance-blister?

As before, you are overly worried about exposures that had little or nor risk for any STI. The chance of either syphilis or herpes from the exposure is zero or close to it. However, your most recent test results are meaningless:  it takes 6 weeks for syphilis blood tests to turn positive; and 12 weeks for HSV2s. However, HSV2 is not transmitted by oral sex and syphilis rarely is. And absence of symptoms is good evidence you were not infected with either one. You should look for herpes blisters or the syphilis sore (chancre) at the genital and oral sites that were directly exposed to your partner.

To be maximally safe, you should have another syphilis test 6 weeks after the event. The blood tests for are not very accurate and therefore we advise against HSV testing after any exposure. However, since you have started down that path, it makes sense for you to have another HSV2 blood test 12 weeks after the event. Almost certainly both the syphilis and HSV2 repeat test results will remain negative.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD