If a woman has an irregular period and she takes a pregnancy test and it comes back positive is there a chance it could still be negative?

There are very few reasons for a positive pregnancy test 1) you are pregnant 2) you've had medication that has the HCG hormone in it (infertility drugs normally) 3) you read the test after the time allowed in the instructions so now the result doesn't count 4) chemical pregnancy (results in early miscarriage) 5) an HCG producing tumor.. very rare having an irregular cycle won't make you have a positive test when you are not pregnant, most likely you are indeed pregnant ~pawsalmighty