How "true" is my blood work for sti panel and hiv 6.5 weeks after encounter? worried about hiv. had symptoms at 8 weeks.

Probably conclusive: Time to conclusive differs between STDs. For HIV, it's 4 weeks for the 4th generation ("duo") test; neg at 8 weeks and overrules all symptoms. And 8 wk is much too late for onset of HIV symptoms. Gonorrhea/chlamydia testing (urine or vaginal swab) is conclusive anytime after 4-5 days. Syphilis 6 weeks. HSV blood tests 16 weeks, but herpes testing usually not recommended after only 1 exposure.