10 days late, negative tests

We have been TTC for the last 8 months, I've been tracking everything and usually regular as clockwork give or take a day. Usual 28 day cycle, am now on day 38 with no signs of period and I've now taken 2 tests and both "not pregnant". 

How long should I wait to test again?

How long should I wait to go to dr?

I thought this would be the easy bit, it's late you test.... I'm worried something else is wrong.