Question about doctor

So I went to doctor and they said I had a yeast infection. I didn't ask for a STI test even though I should because my boyfriend cheated on me. So my question is, would that doctor have known the difference between a yeast or an STI without me asking to check for a STI? I know I need to get tested and I plan to but just wanted to know if doctor could think it was a yeast when it was something else.