So confused??

My first day of my last period was January 2nd - which my period lasts for about 4 days. 28 days from the last day of my period to the first day I am suppose to start. I was suppose to start my period January 30th or 31st. I took a pregnancy test February 8th, came back negative. I went to the OB/GYN today - & it came back negative (a urine test). My period is always regular... It has never been this late. It's disappointing not knowing why my period is late. I haven't had any bleeding, no cramping. Nothing... Just my uterus being sore. I'm healthy, no stress, not taking any medicine.. ( no BC ) . Just someone please help me