it is possible that you are pregnant I would wait until you are suppose to start your cycle again and then take a test.
You could also be going through menopause but the best way to find out is go to the dr I think there are some blood test that they can run to see if it is menopause or not the test you took last week may have been to early to show anything. or it could have come back neg. due to human error or it may be menopause like I said the best way to know is see your Doctor
Are your periods regular or have you started having some irregularity and other perimenopausal signs? It sounds like you probably tested too early if you are not due to start your period yet. The blood test is more accurate than the urine one but it still may have been a little too early. You should be able to do a hpt once you pass the date you are due to start your period. All that being said, this could all be perimenopausal stuff. It is common for women to miss periods, have irregular periods, and have scant periods before their periods stop for good with menopause. It sounds like you should wait a few days. After the first of September, you should probably have another blood test done to rule out pregnancy. Your doctor can also do blood work to check your hormone levels and see if you are entering menopause.