Confused

Chloe • Our 4th baby is due Nov 18 ❤️ 👦🏽👧🏼👶🏼
I am 18 DPO AF was due 8/11 normally have a 31-33 day cycle 
Have had two BFN since. How long should I wait before testing again and/or go to the doctors? 
Only times I have been late is past pregnancies and a chemical pregnant.