My girlfriend took a pregnancy test three days after conception and it says positive with a very faint line should we trust it that early? no kid please

Maybe,maybe not: These tests can be misinterpreted, false positive or false negative. They are more likely to be false negative early on then false positive, but interpreting what is thought to be a faint color change is not definitive either. I would repeat the test with a standard brand hpt, not the dollar store variety, & if concerns remain have the blood test run.