Yellow vaginal discharge, no yeast infection, uti or sti, now sudden, severe lower back pain. pcp can't find anything wrong. what next? have iud in

Infection, PID?: Colored vaginal discharge usually means infection. This sounds like pelvic inflammatory disease (PID), perhaps due to the IUD -- not common but it happens. Also get retested for gonorrhea and chlamydia (the tests miss some infections) and DNA test for trichomonas (other tests miss many trich infections). Consider requesting referral to a gyn who subspecializes in infections. Do it all ASAP.