Can stress cause pregnancy symptoms?

I've been under tons of stress all month; I had a board exam to worry about, after that I was sure that I had contracted a serious illness, and almost instantly after that, I suddenly became convinced that I might be pregnant. I had no good reason for thinking this, but soon after I developed few symptoms like mild nausea that lasts all day and an odd taste in the back of my mouth. I took three pregnancy tests and all were negative, but I think maybe it was just too early to take them since my period isn't due for a few more days. I think my anxiety is causing me to think that every little seemingly odd thing happening is a sign of pregnancy, but I just don't know. It could be stress, but then not knowing causes more stress which exacerbates the symptoms. If it is all just stress/ all in my head, would I get symptoms that I didn't even know were pregnancy symptoms (like the bad taste in my mouth)?