If you were pregnant from sex in August then you'd be showing already. I went through this the summer of 03. It's very disturbing I know. If you can't get the idea out of your head do the pg test anyways, just because.
In the same area as the uterous is all the intestines. Sometimes they move around. That happens alot with those diagnosed with IBS. But it also happens because of parasites. We are all exposed at times, and it's easy to get them. What you do is go to your local organic foods store (or natural products store) and get l-cysteine and green Black-Walnut hull with Wormwood and cloves (comes as a mix in gelcaps). For both take 3 pills 3 times a day. (you can get more info by looking under Dr. Clark's parasite cleanse) In a rather short time you'll see "things" in you BM's. Those things are the parasites. They can be long and stringy, or be round, or look like grains of rice or seseme seeds. There's different types. Once you get rid of them you intestines will calm down alot!
If you'd like an e-mail buddy let me know. I've had a false pregnancy and it's confusing and emotionally exhausting. I'm always willing to help others whenever I can.