I may be inaccurate, but if a blood test comes out negative, then I do not think you can be pregnant. Again, I may be wrong, but I think a blood test is always 100% accurate? For whatever that is worth! ; )
Good luck!
It is possible, but unlikely. All you can do is wait. If I were you, I would do a test every five days or so until your period appears. If you miss another period and don't test positive at home, then see a doctor again.
Good luck!