Need help and advice.

I was recently blessed with a BFP and we were jumping for joy. But just earlier today I went to the doctors and they did another test and it was negative. But when I told them all of my symptoms like nausea, sore swollen breast, missing my period for almost 4 months and horrific lower back pain and terrible heart burn and sensitive smell they told me that I was most definitely pregnant. I don't know what to believe anymore. I'm losing hope. Why would the test Come back negative after I just had a positive? And yes I know you guys are probably thinking its a false positive or an evaporation line or even an ink run. I showed the nurse and she even said it was a positive. But what is wrong? Is my pee abnormal? I need advice.