HI I Have A Birth Control Implant And Have Read

HI I have a Birth Control Implant and have read articles that over 600 women have already gotten pregnant while on this birth control method. I already have one child which I conceived while on a different type of Birth control. I was on a double round of Azithromycin and we didn't use a back up method. that was about 3 weeks ago. over the last two weeks I have become increasingly Nausea, dizzy spells swollen and tender breasts. I have taken a few Home pregnancy tests which all came back negative. and Monday just got a blood test which also came back negative but I still have the nausea and everything and it feels like I'm Pregnant. Could I still be pregnant?