Help please.....

My husband & I have been TTC baby #3 for about 3 years now! My periods are pretty regular, usually no later than 4-5 days. I'm on cycle day 42 & 6 days late, i tested on sun & Friday & both negative...do I keep waiting it out, test again, go for a blood test? 
Update: Both tests were taken between 5:00-7:00pm if that may have anything to do with it...