Hi I have been on birth control for 4 months then this past month I switched to yaz... been taking it everyday at the same time and also use a spermicide with it, and now a day late on my period what do you think about me being pregnant?

Unlikely but possible. Not because is 100% effective. It can't hurt to take a pregnancy test tomorrow using first morning urine just to play it safe. My period usually comes on weds or thurs. but its not entirely unusual for it to be "late" and come on Friday or even Saturday.