Should I go to dr for a blood test?

AF is currently 3 days late. She is always on time. Never late. I have taken several home tests and gotten BFN. When I was pregnant with my first child I was on birthcontrol and did not know until I was 26 weeks pregnant. They gave me a "pee" test when I would have been 3 months pregnant and it came out negative. So I continued my birthcontrol. It didn't show on the home tests till almost 6 mo pregnant. Should I go to the health department and get a blood test? Or should I go to the obgyn and ask for an ultrasound if AF hasn't shown up with in the week? What do y'all suggest??