My urinalyses have shown RBC and WBC, but culture was negative. I have been having flank and abdominal pain, at a loss currently?

Stone? STD? Other? Non-infectious kidney disease could be possible; it would be important to know other urinalysis results, blood tests for kidney function, and perhaps imaging of the kidneys to check for stones and other abnormalities. Gonorrhea or chlamydia, but of course only if at risk for STDs (new partner, partner with other partners, etc). Other possibilities as well. Discuss with your doctor.