Negative test but a late/missed period

AM

Hi all! So my period is SUPER SUPER regular, has been since I got it 9 years ago. My husband and I have been trying to conceive for about 5 months now but this month my period is 8 days late (this has NEVER happened before) I don’t have any stress in my life currently and have had no major lifestyle changes. I’ve taken 4 pregnancy tests and all of them have been negative. So my question is, how long should I wait before going to the doctor? I plan to test again when the 2 week mark hits but I’m tired of spending money on negative tests. Anyone had this happen to them before?