Please read i dont know what to do help?!?!

I went to the doctor yesterday to have a normal check up and bc i might have gotten a yeast infection and also to ask why my period hasn’t came since last December 2018. Being pregnant has crossed my mind so i took a pregnancy test a month ago but showed negative so whatever i wasn’t pregnant that was ok bc I’m 20 years old plus my partner had cancer and he told me there is a high chance he might not be able to have kids so we been having unprotected sex for over a year now and he is 2years cancer free so at the doctor visit yesterday they asked do you mind if we do a pregnancy test with your urine and they did it and it was positive i said it cant be can you run it again and it showed positive again. So we got really happy i told my parents i told my partners family all our hopes up

i went to and ultra sound today but they couldn’t find anything! At all the doctor said i wasn’t pregnant like a definite NEGATIVE! So i told him can i do a blood test we were all super devastated so we did a blood test and it showed a faint line but the doctor said it might show positive but you’re NOT pregnant...... so WTFFF im so sad i thought it was going to be a miracle baby but i still have a tiny bit hope because ALL the tests showed POSITIVE!! what should i do???