Std test for gohnorrhea and chlamydia came back negative from quest. i had already been taking doxycycline for 3 days prior testing. could this cause a false negative? should i retest for these two? bloodwork was negative for all other stds?

Probably you were not infected. Doxycycline is always active against chlamydia and sometimes against gonorrhea. However, the tests are for bacterial DNA (gonorrhea) and RNA (chlamydia), which remains present for a few days even with successful treatment. So your negative test result makes it unlikely you were infected. If you complete 7 days doxycycline, there is no point in retesting.

The chances for false negative are very low in this scenario . But if worried or have a high possibility from exposure get retested