Should I go to the Drs?

Af was due on the 3rd Jun but nothing, I have lower back pain nasua and dizziness. I have done 3 home tests the first was negative the 2nd had a faint positive but the 3rd was negative again. I have no idea what's going on. I'm wondering if I really am not pregnant but then I can't understand why af is so late as it's never happened before but at the same time I'm wondering if my hcg level just isn't high enough. What do you think?