pregnancy tests

Emily

ok so im 5 days laye for my period but there pretty irregular so thats not that exciting but just incase i took a pregnancy test last night (middle test) it showed up negative but i left it on the sink this morning went to throw it away and it was possitive so exciting so i took two more one was the same brand the other was a clear blue week estemator both negative .. ?? so am i pregnant or does leaving them out over night change them?