I knew something was going on with my first. I had fake hunches every month, but when I was actually pregnant it was different. I even ordered a beer a few days past O and just couldn't bring myself to drink it. I was way more chilled out in the tww, too. Didn't feel the need to test a million times, skipped days, etc.
With this one, I didn't have as strong a feeling, but I had the same kind of Zen outlook after obsessing the previous month, and that made me really suspect I was pregnant.