Every 2 months I get severe nausea & vomiting. All tests are 'normal'. Doc says its just bad luck w/ stomach flu. Could there be another cause?

Sure. Guy or gal? If gal, could be related to hormones, menses, ovulation (perhaps just from one of the ovaries, thus every other month). Check timing of symptoms with menstrual cycle. Could be cyclic vomiting syndrome; could be other triggers for the symptoms, could even be migraine related. Could be other stuff too. Keep looking.