Pregnant?

Help! I've taken 3 EPT tests over the course of three days along with one first response this morning. I'm 6 days away from my missed period. The EPT tests all have very faint lines but they didn't show up for about 1.5 to 2 hours after taking the test. I've had this happen before when I had a miscarriage.  (The faint lines showing up late) they are colored lines not evap. The first response still says negative.  What should I do?