I am 18 DPO

I have tested twice and the first one was maybe a vvvvfl and I tested this morning and do not think there was a line unless it was a vvvvfl. I am super regular and never this late and don't know what to do. I have been nauseous and having mild cramps and going between being constipation and diarrhea! How many days late should I be before going to the doctor