What Causes The Cause And Treatment For Vaginal Infection?

Hi...I have been constant battle with yeast infections.i have been using apple cider and garlic to treat them. I finally thought I got rid of one but now I have this wierd thick discharge that smell like rotten eggs.i have an open relationship and have another partner besides my husband but I don t use condoms with either of them but I don t allow them to cum inside me.we all got tested for stds a few months back but I can t figure this out. Could I have caught something?