Late period. Negative tests

Just wanted to get opinions. I am 4 days late. I have taken 4 preg tests and all negative. I am so pregnancy symptoms such as sore breasts back ache here and there and slight naseau every once in awhile. But I do get cramping off and on like my period is going to start. I have a one year old and I cramped with her on the beginning also. But i am just so confused as to why I haven't started and all these neg tests. Any insight?