Ok. A month ago I took an EPT at my friends house and watched it for 3 min. and it wes negative. So I quit worrying... But I threw the test in her trash in her room... and apparently she doesn't change it often cause she called me last night to tell me I needed to take another test cause she saw the test in her trash and saw it Had 2 LINES meaning it was positive. But when I took it a month ago it was negative... Could it sitting make it change or did I not watch it long enough? The irony is about 2 weeks ago I had some heavy bleeding off my period and then my period was a few days late... and Before she called last night. Yesterday morning I took one and it was Negative again...

It depends on the hormons that you have. For example, when I took my pregnancy test I was estimated 5 weeks. The test came up positive instantly. However, my cousin did not make enough pregnancy hormons to make the test come up positive. So she got a false negative. Always take two test just to be on the safe side. Now I am 25 weeks pregnant and I still have my pregnancy test, and the test still shoves a positive. It is likely that you did not watch the test long enough.

Well the one I took yesterday was negative... And stayed that way all day long

Yes, the result you get reading a test after the time frame stated for that test is not considered accurate. Some tests are more likely than others to show what appears to be a faint positive when read later on. This is why it is important to follow the directions exactly.