Is there a possibility of me being pregnant?

Ok so I had unprotected on the 8th 10th 13th and 14th of this month. I have a regular 28 day period and was supposed to start yesterday, but I still have not started. Usually, my get really sore a few days before I start, but that hasnt happened either and I havent been cramping. My stomach feels wierd and i randomly get nausiated. I thought that may have been due to nerves and the stress I am currently under, but Im not so sure now. I took a pregancy test yesterday evening. My bladder was almost empy but got enough for the test, It came up negative. I got it from the dollar tree, dont know if that is ok or not. Please tell me what you think.