I took a urine test and was positive for leukocytes. i was given antibiotics that didn't work. another doctor is saying it may be an std. is this true?

Unlikely: Leucocyte urine test can be positive if vaginal epithelial cells or smegma gets into urine specimen. Another explanation could be that you have a UTI with an organism resistant to antibiotic prescribed. Best to have urine culture with antibiotic sensitivities when UTI suspected or urine +ve for leucocytes. STDs in women tend to affect vagina & genital tract. Please use protection in future.