Negative test but still no period!

So between 4 different apps, I was supposed to get my period between 03/14/14 (earliest) and 03/17/14 (latest).  Both days came and went, yet no period.  On Tues 03/18/14 I took a hpt, but it was negative.  It's now 03/23/14 and STILL NO PERIOD.  I've never skipped a period; and the latest I've ever been was 3 days.  On Thurs 03/26/14, the hubby and I have our first appointment with a fertility specialist, but I'm not sure if I should try another hpt again or wait for our appointment to take a blood test.  I guess I just would like some feedback of whether anyone else has encountered this same situation or not, and if so, what was the outcome?!