PLEASE HELP!! Is there still a chance?

I am on day 38 of my cycle and still no AF. 35 days is be longest my cycles have been in the past. I've taken two tests (clear blue and First Response) and both negative. I've had some mild cramping, more like little twinges, for the last week. My boobs feel a little fuller but aren't very sore. Is there still a chance I could be preg and how much longer should I wait to take a test?? My body better not be playing tricks on me!!