I got tested (for every std) 3,5 months after having unprotected sex. it came back negative, but should i get re-tested? how likely is a false neg?

Retesting: Often testing for some std's like genital herpes, hepatitis C, or even hiv will not show up on initial testing. In these circumstances, retesting at 3 or 6 months is appropriate, especially if you believe the partner was "high risk."

No worries, no STD: All the standard HIV lab tests are very reliable, and 3 months is long enough for conclusive results. The 5 month tests weren't really necessary. False negative reuslts after 3 months are virtually unheard of for some tests (e.g., HIV, syphiils, gonorrhea, chlamydia) and rare for others (e.g., herpes). You can be sure you weren't infected with any of the STDs for which you were tested.

Not necessary: If you would feel better,retest for HIV only