Early signs of pregnancy AFTER you take a test and it says negative?

Last time I had sex was June 17,2011. I took a pregnancy test between the 18 and the 26th of June 2011. The results came back negative.... Was it too early to detect pregnancy? I haven't gotten sick, but I do have a little abdominal pain. As well as nausea (haven't thrown up yet) and gas. Between the 26th of June and the 1st of July (today) I got a YI. Im currently treating it, but I read you could get a YI from hormone changes. BUT, I go to the pool every Wednesday at work...so that could be the cause of the YI. I try not to think about it.... maybe this is all mental and im not pregnant. Is it still too early for me to test? Oh, i also have irregular periods so i can't count on that to come save me!