Confused

So I’m 6 days late for my cycle and I have been getting negative home pregnancy tests. I had to take my little to the drs office yesterday and since I was there I asked them to do a blood test just to be sure. We’ll they called today to tell me it came back positive. I’m very excited just a bit confused as to why I’m getting negative urine tests. I even got a negative today. Also this has never happened to me before. With my first two I had positive home tests the day after my missed cycle. Any input is appreciated!!