I treated gonorrhea. negative with urine test 10 and 20 days after injection 500mg cex. and negative swab throat + vaginal (same swab) at 32 days. on cdc website they say we need to retest after 3 months of treatment. do i really need to do that?

Good question! Statistically, the chance of repeat gonorrhea (or chlamydia) is quite high, and testing at 3 months picks up most such repeat cases. Obviously it depends on each person's sexual risks, but many people cannot be certain about risk -- for example, whether a partner has other partners. If you are certain there is no risk at all (e.g. no sex since treatment), testing isn't needed.