17 DPO & no sign of AF

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I’m 17 DPO today, my nipples are sore, no sign of AF. I took 3 dollar store tests over the last 3 mornings, all 3 have been negative. Is it because the tests are not good enough? Am I out yet? Anyone else go through this? Typically, I get my period within 2 days of my last period start date, so last month it started on the 16th, this month it should have started on the 18th ish. It’s the 21st today. Just confused

Also I wanted to add, twins run in my family. I have twin siblings, and my grandpa is a twin, my mom got pregnant with twins twice. I wanted to add that because I know sometimes you get a false negative with twins due to your HCG levels being too high; is this common or not really? This would be my first pregnancy.