PMS and early pregnancy are pretty much impossible to distinguish. I was CERTAIN my period was coming at any moment for the full two weeks after my IUI. The only differences was after about day 10 I was SO nauseated I could barely stand it. I mean, at one point I was in a cab and I thought I was going to have to ask the driver to pull over so I could puke! But even that day I kept running to the bathroom to see if I had started. I didn't and I still haven't!