2 mossed periods and still no postive

I need some advice ! I have now missed 2 period and have been having pregnancy symptoms( nauseous, sore boobs, tiredness) but every test I have taken has came back negative with my daughter I got a postive the day of my missed period so when I found out I was I only 5 weeks! My ob won't do a blood test unless I have a positive urine test and they all come back negative! What should I do ?:(