Pregnant?

So Tuesday early afternoon I took a first signal pregnancy test & it was positive. Then A couple hours later I took A clear blue & it was negative. Now I should Say that this was 4 days before my period was even due but I'm not sure what to think & have waited to test again. Also my symptoms are mild cramps, sore breasts (while h happen even for my period) I have had a hard time sleeping for 3 nights & back pain. Anyone have any idea what could be up w a positive & negative within hours?