Could I possibly be pregnant?

Okay so my soon to be husband and I had unprotected sex on 6/13/2011. I have irregular periods but for the last three months it has been constant. The day I was suppose to be ovulating was on the 13th. Which I was surprised it happened on the day. After two weeks I checked with Clearblue easy. It came up negative. I waited until today the 30th to check again. Again it came up negative. Could it be just the brand?? My period was suppose to start on the 27th. I have had sever nausea all different times of the day since about 4 days after possible conception. Certain foods the smell alone makes me sick other food taste disgusting. And last night my feet started swelling really bad. I've never really had them like this. They feel like marshmallows! So what should I do? Change brand? Or is it possible that I'm just one of those people that HGC (think thats what it is called) wont show up unless I do a blood test?? Any help is greatly appreciated. The sooner I found out the better and if I'm not I'd really like to stop worrying :-p. Thanks!!