Confused!

Rachel • I`m 25 from Florida and TTC baby #1 with my wife.
I am now 18 dpiui. I had a blood test done at 14 dpiui and they said it was negative. Is there any way I could still be pregnant? I have not been feeling myself (nauseous, tired, irritable). My period should have been here by now and are pretty regular. Just wondering what's going on...?