It usually tells you of the pregnancy testing kit how long to wait for an accurate reading to be achieved. If you followed the instructions on the pack then it should be right. But if you feel that you did not follow the packet instructions accurately and are still concerned, then like thatquietgirl says, take another test after waiting another week.
It could be that you may have a hormonal imbalance or that you
you may have anaemia. Polycystic ovary syndrome can also mess periods.
If you have not been eating correctly and have become anaemic that can mess up periods and sometimes they stop.
If your periods have not normalised within the next couple cycles, then I suggest you see your doctor and take your monthly cycle chart with you to show the doctor.
Best wishes.
Sometimes our hormones just differ from month to month, which could account for the brief period as could stress, illness, a change in diet, or a change in exercise. However, you could wait another week and test again if you believe there's any chance.