How early can I get a blood test done to see if I'm pregnant...

3-4 wks after period. A blood pregnancy test can be positive as soon as 10 days after fertilization. This is usually just before your period is due or soon after. A urine test done first thing in the morning will become positive about the same time.
10 days. A pregnancy test can be positive about 10 days after conception. A urine pregnancy test is about 98 to 99% accurate - there is usually no particular benefit to having a blood test for a pregnancy test.