Has anyone had mulitple BFN's and were still pregnant

Cassi • Momma of Three Graci 5-7-15 Graeson 9-7-16 Gabriel 8-6-19! Angel Momma of Two Nov 2015 and Twin B Jan 19 2016!
I was wondering does it take longer for some women to test positive than other cuz ive had multiple BFN from dollar store tests and i M now 4 days late for AF im loosing hope here!!!