My face swells after taking ondansetron and my doc says im allergic to all anti nausea drugs now, is that right? was it just a side affect?

Not right.: Sounds like allergy. Ondansetron is a 5ht3 receptor antagonist and probably shares immunogenic potential with other members of the 5ht3 class. All those medications are antinauseants and all end in -setron, e.g. Granisetron. There are many other anti nausea meds which work at different receptors and do not likely share any immunogenic potential. But Metoclopramide has some 5ht3 activity.