It's been different all 3 times.
W/ my first, I was still in college and in party mode. I went to a party and couldn't stand to even smell the alcohol, so I didn't drink. Was wondering what the heck was wrong with me. On the way out, someone was smoking a cigarette and I almost puked. The MJ smelled oddly good to me, though. :LOL A few days later, my boobs hurt so bad I couldn't stand anything touching me, even my clothes or the shower. I started suspecting something. And then a week later I got morning sickness. I have no idea how far along I was when these things happened. I had been on Depo Provera and it wasn't all that long after missing the next dose (decided to quit b/c of side effects). I hadn't had a period yet and was told it could take months for my fertility and cycles to return and no bc until then.
W/ my second, we did the deed w/out a condom at a bad time and I realized it the next morning. Didn't really feel different until around when my period was late, but I knew I was pregnant the morning I woke up w/ the realization. I do know that when my period was late, I had been putting hot sauce on everything for a few days. My dh knew I was pregnant when I started doing that. I never ate spicy foods EVER from the time I got pg w/ ds1 till I got pg w/ ds2. (isn't that wierd?) That was the first pregnancy he'd seen, but he's very intuitive. LOL!
W/ #3, I had PMSx100 before my period was even due. Then I had implantation spotting 2 days before my period was due and I kinda knew (even though I'd never had implantation spotting before and didn't even know that's what it was.) I got morning sickness about the day my period was due. I had no reason to suspect I was pregnant since we had been using the methods in Take Charge of Your Fertility and had not messed up. I chalk this baby up to a leaky condom. No other explanation. We never noticed anyhting wrong w/ the condom either.