How soon should a positive result show up on a regular pregnancy test, not an early dectection pregnancy test?

I was 3 days late on period, so I took a regular detection pregnancy test from the dollar store. It was positive with a very, very faint line. So being unsure, I went to Walmart and got an early detection pregnacy test. It was positive. So the next day I went to planned parenthood to fill out paper work for insurance reasons and their test came back negative. Im really confused and not sure what to do. I told her I took two tests and they were positive. I'm now 5 days past my period, I took another test and it was positive. Why is planned parenthood's test not picking up the same results?