I've just been diagnosed with gardnerella vaginitis & a yeast infection. I was given diflucan (fluconazole) & flagyl. Should my husband be treated also?

No. These are not expressly sexually transmitted infections. The pathophysiology has more to do with the micro-environment of your vagina that allows overgrowth of what some would argue are normally commensal flora. Diflucan (fluconazole) is for the yeast and Flagyl is for the gardnerella spp.