4days late for Af bfn?

Ok so i found in january i have pcos ive been on metformin since then my af was pretty normal before i even found out i have pcos but now it is missing was suppose to start the 10th an no sign of it i have cramps an sysmptoms of my af but no af is this normal i took a test today it was a bfn really confused my af has never been this late for me besides a day or two but most of the time im early please help me