Weird premenstrual symptoms

Hi all,
I have been feeling a bit funny lately and thought I would ask for your expert advice on what may be going on.
I typically only have nausea when I am pg. I don't have it before or during my period. But, in the past few months, I have noticed these twangs of queasiness coming over me right before my period, pretty much in the 2WW. And of course that makes me very anxious, wondering if I'm pg or what. (But I was not!)
By the way, when women do have pregnancy nausea, how early can it start?
Anyway, wondering what may be causing this and why I am experiencing this at this stage of life. Any input would be much appreciated.
Taylor