Feeling confused??

My husband and I are TTC. I haven't had a period since December and I've taken multiple pregnancy tests. (all come out negative) but still nothing. We pretty much only have sex when I'm ovulating. And still nothing! I haven't been stressed at all. Financially we are good and life is great otherwise. I dnt understand why I'm not having a period or why I'm getting negive tests. Anyone have this happen before?