What Causes Delay In Menstruation Other Than Pregnancy?

Hi I am having symptoms of Pregnancy but I have taken 4 test and all have been negative. I am experiencing Nausea and vomiting, sore breasts, fatigue, dizziness, moodiness, clear vaginal discharge also I haven't had my period. My only problem is I am not sure if I am even far enough along to even be taken the pregnancy test. Could I still be pregnant even with the negative test?