Why Is My Period Late If I Am Not Pregnant?

I have missed my period, it should have started on the 19th and ended on the 24th (yesterday) but it hasn t been and there are no signs of it coming, I have never missed a period before and have been having unprotected sex with my partner for exactly a month today. I have taken 14 pregnancy tests over the past 2 weeks and they re coming out negative. How likely is it that I m pregnant and how will I know without having to have a blood test? I already told my partner I thought I was pregnant and he s really excited so I don t want to confuse him, especially since I m slightly convinced that I am. I don t want to worry him by having to go to the doctor because then I ll have to explain about the tests being negative so he ll think I m definitely not pregnant which I still think I could be, but I do need to know as if I am I need to make some changes in my life. I m not sure if I actually have pregnancy symptoms or if I ve just talked myself into thinking I do, but I m definitely urinating more frequently, I feel like I have been feeling tightness in my abdomen and I ve been getting a bubbling feeling. I go light headed sometimes when I stand up and the room spins and I feel sick then after literally only a couple of seconds I m fine again. I m really confused because I don t know what else it could be and I ve taken a LOT of tests so is it possible that they re all wrong?