You know I had the samething happen to me with both babies. I swore I was pregent, well they kept telling me I was not. Then a month later it turned out that I was. If you think you are then you should go see your OBGYN they are the only ones that can tell you for sure.
I'm in the same boat. I had a period, I've taken 4 pregnancy tests and they've all been negative. But I swear I feel my uterus growing and even having braxton hicks contractions. It's really freaking me out. I have a Dr.'s appointment on Monday so I should be able to find out for sure then what is going on. I hope you figure it out too, this limbo period just sucks.