Some people say they just "knew" the day or two after, and others say they had no symptoms whatsoever.
With DS1 I got a BFP in the first cycle. I fell ill pretty much immediately. Had hyperemesis gravidarium until 6.5 - 7 months along. I had to wear a subcutaneous drip of anti-nausea meds 24/7.
With DS2, we were more relaxed. We "tried" for two months. One day I felt faint in the shower and that's what triggered me to test. BFP right away, and it turns out I was already about 2 weeks late.
This time around, it's been 6 cycles and I'm starting to get impatient. I know that's horrid of me - I truly admire all these ladies who endure month after month of the emotional (and physical) roller coaster.
My inner nerd is taking over and I'm going all scientific on this one. If this month doesn't take, I think I may pay my OB/GYN a visit and just make sure everything is ok.