Soooo is it possible?

So I am 20 days late in my period.. I’ve already went to the dr and she gave me meds to help start my period. I finished them earlier this week, when I went to the dr, they did a urine test to see if I was pregnant, but it was negative. They did blood work but not for pregnancy test. Is their a chance I could be pregnant and they missed it? I’m just curious because the only time I was ever this late was when I was pregnant with my oldest child. Should I buy a test and take it in the morning?