If you tested for STDs one month after your exposure, some of your test might be not accurate at 100%.
One months is enough time to wait before testing for gonorrhea and chlamydia.
But for syphilis, it would be good to wait at least for 6 weeks, and if you get a negative result, it would be interesting to retest 3 months after the exposure, as there are people that take longer to show a positive result.
If you tested for HIV using a duo combo ag/ab 4th generation test, your result was accurate, as you would have just need to wait for 28 days after the exposure. But if you used a normal 3rd generation antibody test (finger-prick) it would be accurate 3 months after the exposure.
For herpes, you can test 3 months after the exposure.