I am 4 days late and all negative tests.?

I dont know what going on!!! I had the 3rd-6th and 8th and 10th of May as wells has much in April. ALways during my ovolation time. Not using any kind of protection nor pulling out. Im am 4 days late and all i have gotten is negative tests. I am not stressed. Im a very happy go lucky person. I dont have many worries right now except my Husband can be rotten somtimes! I dont really have any sytptoms but small cramping here and there, tired a bit, tender tip of the but not bad only if they are touched and odly a few nose bleeds! which i never get. my period had come like clockwork every month. Never a day early and never a day late. I cant possilbe be pregnat being so late and have not one positive test. ( all have been the 5 day sooner ones). Dose anyone know what else could be wrong with me? Thank you!!