How late without a positive?

I am like 11 days late. I took a few pregnancy tests all negative. Had hcg tested last sunday was 7, so doc said not pregnant. Anxiety, medication, etc. Could be delaying my period, never been late in my life except when pregnan(even stopping same meds never made me skip a period) i am 40 tho, i heard about late ovulation/implantantion etc, i dont even think this is the case, when is too long to go w/o period and get it checked? What should i check for? Blood panel everything was normal. Appreciate the insight