My Nexplanon Birth Control Expired July 2 And Had Unprotected

My nexplanon birth control expired July 2 and had unprotected sex before I got the new one in July 12. I've had 3 implants and my menstruals are usually heavy and last long, in the last 6 years I've never missed a period on this birth control now look feel and have a round belly, is it possible that I could of got pregnant when it was expired? The hormones in the birth control cause pregnancy test to have a false negative and I have taken 4 tests and they're all negative but I feel and look pregnant. Is this possible to get pregnant on an expired BC?