Negative hpt, actually pregnant?

Hi guys,

I've been hearing a lot of stories lately about women who have taken hpt's and tested negative, only to go to the doctor and find out they are actually pregnant through a blood test or ultra sound. Is there anyone who has gone through this that can share their experience? How much does this actually happen, and does it have anything to do with pcos? I haven't had a period for 2 months now, and have had certain pregnancy symptoms off and on. I plan on going to the doctor to figure out what's going on, but in the meantime I thought I would make a post for anyone who has experienced something like this. Thanks in advance!