It's definitely possible - that's my story and I'm sticking to it!
Seriously though, it's not over until

shows up. It's possible that you Ov'd later than you thought so if you are pregnant, you might not be as far along as you think. With my son the HPT showed positive on 11DPO so I'm thoroughly annoyed that I keep getting negative tests! (Of course the thought that I might NOT be preggers has not entered my mind!

)

is due tomorrow so we'll see!
Good luck!