What happens when i take a pregnacy test and it turns up positive and later that week another that was negitiv

I took it and it was positive and a week later took another and it was negitive. I don't understand how that could happen.What happens when i take a pregnacy test and it turns up positive and later that week another that was negitiv
All tests have a margin of error for false positives. If you have any doubts go to the doctor and have another test done.
the test could have been bad! i took 7 when i was pregnant with my son and all of them said neagative! if you use an at home test it is best to use your first urine in the morning! if all else fails go to your doctor and let them test you!