it can be but if she's getting properly tested for vaginitis odds are it isn't. covering all your bases is always a good idea!
I've been wondering if i was the ejaculation. If so, is there something that could be done? I'll tell her about the tampons.
would herpes be causing the problem?
vaginitis is pretty common in females. you can try something as simple as protected sex only for a few months to see if your ejaculate is altering her vaginal ph enough to allow overgrowth of yeast and bacteria. sometimes it helps, sometimes it doesn't.
have you both been tested for herpes? it's typically not a part of routine std testing.
if she is getting vaginitis a lot, she shouldn't be using tampons.
grace