CD44 and BFN

I'm currently on CD 44, about 15 days late for AF. I've been testing about every 3 days and have been getting all BFN. I have no symptoms of PMS or pregnancy. Usually my boobs are sore for a week before AF and I've had nothing. I've had a little more CM than normal. At what point in time do I seek medical help or testing? My cycles usually are 28 to 32 days long. I just don't know what my next step is. I don't feel like I could be pregnant with all the BFN's.