I tested positive for chlamydia and bv 4 days ago. i've been on antibiotics, many symptoms have resolved but still am having burning urthera what could be the cause? urinalysis negative for uti?

Probably Candida or yeast infection related to antibiotics

If your urine culture was negative for a UTI, it's possible that your urethra was affected by the STD & this inflammation is slow to resolve. I recommend continuing your antibiotics, drinking plenty of water and waiting to see if urethral symptoms resolve. . If not,repeat the chlamydia test or consult a urologist.