Negative blood test positive urine test?

Almost two months since my last period so i went to the dr and took a urine test and it came back positive she said she wanted to take a blood sample to see how far along i was and then she called me the next day and said my blood test came back negative that she wanted to retest me in two weeks...i was really excited and it was crushing news im scared to go back now...has anyone else had this happen? what were the results?