You know you could be PG. When I was PG with my DD, I had ALL of my usual AF symptons and a ton of negative PG tests. That went on roughly 3 weeks until one morning (Easter Sunday 2002 in fact!) one ACTUALLY showed a BFP!! Then I was in denial that it was a BFP and made my hubby go out and buy 3 more tests and they ALL showed that I was! But that wasn't enough for me, I still set up an appt at a clinic where they did sonos and that is when I saw the sac and they determined I was about 5 weeks along. So I was PG the whole time I was testing negative.
Moral of the story, don't assume you're not PG until you get your AF visit because you NEVER know! Good luck!