Yeast infection, did my boyfriend cheat?

My boyfriend and I always have unprotected sex never any symptoms... this Saturday past after having sex I immediately begin itching and discharging white clumpy stuff.. I ddnt panic just went to the dr Monday and he said I had a yeast infection.. this was my first time with one ever.. anyway my sisters and girlfriends insist he cheated on my unprotectedly.. could I have possibly gotten a yeast infection this way? Thanks in advance