It is unlikely that ur pregnant and it not show in a hpt. Personally I was 5 weeks late just in march and I insisted on a blood test, because I am pretty regular and had 3 hpt's come back neg. The blood test said I was not pregnant. What a hpt tests for is a hormone that your body releases when u r pregnant. The blood tests for the same thing. If you really think that's what it is, go get the test. A level of 8 and under is normal for every woman.... If you're pregnant the first couple of weeks it shoots sky high (somewhere around 20,000 I think, but not sure).. But it is possible....Just not likely. Stress and a lot of other things can make your period late. Good luck!
It is more likely to get a false negative than a false positive on hpts. So if you think that you may be preggo then yeah I recommend you go to the doctor and get a blood test because they are more accurate and a lot more sensative than the hpts. Good luck hope this helps.