I have been dating my fiancé for 8 months. In 8 months she has had three yeast infection, before me she had only one in her whole life. Is it possible it could be me? Why she is getting the yeast infection?

Sure, it is actually possible... you can harbor a yeast infection that she keeps getting. Particularly if you are uncircumsized.

Yes, smoothy is right. Bacteria under foreskin is usually the culprit. Better pull it back every time you shower and wash thoroughly. In fact, and I know this sounds tedious, but if you care for her health and comfort, wash under your foreskin before sex. :)

I'm circumcised,I have never had this issue with past girlfriends.

Every woman's vaginal norma flora is different. Still give it a good washing. Do you use condoms? Is there anything different in what she's doing from before she started dating you to now? Different birth control or even different soap?

There are a bunch of reasons you can get yeast infections. The important thing is to treat it fully.