I have a fishy smelling discharge after an endometrial biopsy, should I be concerned?

Possibly. Any abnormal discharge after an endometrial biopsy should be reported to your doctor, as it may be a symptom of having an infection of the uterus. It sounds like there is a just a bacterial overgrowth, called bacterial vaginosis. Antibiotics and probiotics can help treat and prevent "bv." see your doctor to be sure.
Yes. Possible infection or bacterial vaginosis. Report to your dr for a timely treatment.