How long to wait to test again?

My AF was due yesterday. My normal cycle runs 32 days in length. My last period was Feb. 10th. I took a Clear Blue Easy Digital on Friday and it came back BFN. So, I waited and took another this morning and it was again BFN. I've heard that with the digitals you sometimes needs higher HcG levels for them to be detected, then in the dye +/- or two/one line tests (i.e. first response) I have never used the digitals this was my first time. I have been nauseous, tired and irritable. I normally get a terrible migraine the day before or the day of my AF. But, haven't had one in about 8 days. How long should I wait to test again? Could I still be preggers? Has anyone used the digitals and gotten a "not pregnant" but used the other regular tests and gotten a "positive" ?

I used a regular first response with my daughter 2 years ago, it was not digital..but I was also 6-7 weeks along. I was in denial. :) Thanks!