Er told me i have trace amount of blood in my pee from a bladder infection that's causing false positive pregnant tests, how is that possible?

Possible: Blood in the urine can alter pregnancy test result in that it makes it invalid. They should have drawn serum pregnancy test to rule pregnancy out.

Not likely: I suspect that you have miscommunicated in some fashion. Have your primary doctor repeat the tests. Trace amouts of blood or blood cells will not interfere with the pregnancy test.