Could stress cause yeast infection?

Yes. Severe or chronic stress is known to have a negative effect on the immune system and could plausibly increase the likelihood of getting a yeast infection. Additionally, there have been some studies which support the link between stress and vaginal yeast infections.
Doubtful. I've never heard of stress causing a yeast infection. You should see your ob/gyn or primary care doc for evaluation. Stress can cause outbreaks of other skin conditions like psoriasis, eczema and acne under the right circumstances.