Why did I get two positive pregnancy test at home and blood tested negative? How is that possible?

Different thresholds. It is possible to have positive urine and negative blood. The home urine tests are pretty sensitive- namely they don't miss much. They are looking for a HCG of 20 miu/ml and the blood test is looking for a level of 25 miu/ml. So if you were super early and your level was 22 miu/ml your urine would be positive and the blood negative. Repeat the blood in 1 week and then see, good chance its + !
Two possibilities. In addition to the possibility mentioned by Dr. Klein, it could be that there was spontaneous loss of pregnancy between the urine tests and blood test. About 25% of early pregnancies are lost, mostly due to chromosomal defects in the embryo. Usually the only manifestation is a slightly heavy, delayed period.
Have safe sex, Get HPV vaccine.