Did he cheat?

I had unprotected sex with my boyfriend bc I have the implant. He still pulled out but I started having itching and burning a few days later. Then white discharge. My sister had 2 out of 3 pills for a yeast infection so I took them with no relief. I plan to make a doctors appointment but does this sound like an std? Just wondering bc my sister had a bad yeast infection and just took one of those pills and it went right away and I took the last two with no relief. If so that would mean he cheated bc I haven’t been with anyone except him. I’m so nervous I have an std and that he cheated on me.

Edit bc of someone’s rude comment. I took the pills for a yeast infection bc I have had one before and it feels the exact same.