I took a pregnancy test (one of the cheap $10 ones from Walgreen's)and it says on the instructions "DO NOT read after 10 minutes". After taking the test and waiting the 5 minutes I was supposed to, it read negative. An hour or two later, I looked at it and it was positive. Is there a reason it changed from negative to positive? Why shouldn't I read the test after 10 minutes? Should I take another test? I should be getting my period today or tomorrow (I'm irregular) but my boyfriend and I are very worried. Please help...

The reason you need to read it in the time indicated is that some tests will show an evaporation line later on that can look like a light positive.

See if your period is actually late... then maybe give it a few more days to see if it is just off this cycle. Test then if need be.

First morning urine tends to have a higher concentration of the pregnancy hormone, hcg, so even though many tests today are sensitive enough to pick a positive up anytime, it is usually best to test in the morning to insure accuracy, especially if you are not sure of the sensitivity of the test you are using (some are more so than others). Do be sure to read the test in the time specified.