Does using lubricant (durex) into the vaginal opening right before protected sex (with condom) cause vaginal yeast infection?

No. Unless you are having a reaction to the lubricant which damages tissue leading to secondary infection it will not cause yeast infection. This is very common and predisposed to by antibiotic use, diabetes, immune deficiencies, contamination by a sexual partner, and sometimes just happens. The organism lives in your colon and can get onto the labia and into the vaginal opening.