You should have first discussed both of your history of std's. If you didn't, you should asap. What is even better is that you both get full std panels so you know your status's for sure. It is for her benefit as well as yours. It is not uncommon for people to have std's and not show symptoms.
As for what you think is a fungus, have it checked out by a doctor so you can get the proper treatment. Fungus's are not std's, though some like yeast can be contracted sexually. If she has a yeast infection during sex, it could cause the natural yeast you have in your body to overgrow as well, and voila. You have a yeast infection.
Ask about her sexual history. Find out things, if she have had std's or stuff like that.
To me it sounds like an ordinary thing, maybe even a hygiene thing. Too much sex, the stress it has on your penis, microtraumas, it might be origin of fungus.