STD??

So my former sexual partner recently threatened me bc he claims that he's been itching and burning since the last time we had sex. He says he has a doctors appt tomorrow and he believes that he's gotten and std from me. I want to know how he would have possibly gotten and std from me if I don't have one. I haven't shown any signs of an std and have never experienced and burning aside from a yeast infection almost a year ago. None of my previous partners have said anything about itching or burning and I've only had three partners this year. Would there be any way of me having an std w/o knowing? Or could he have gotten it from someone else or it just be a hygiene problem?