Wait another week and test again.

Did you use any form of birth control?

if you're worried, go see a doctor and have them give you a blood test. For some people, certain hormones that show whether or not you are pregnant either show up later in the pregnancy or are faint at first to give you a false negative result.
All I can really tell you is that I have been there more than a few times.

I had an ultrasound and HCG check up today but the result is Negative

Well that pretty much settles it.
Have you been on birth control before? I'm asking because if you recently stopped it can mess with your cycle.

Its possible you just skipped a period. It can be a very normal thing most women.

No I have not been on any birth control methods.

Relax and see what happens this month.

Missed periods aren't really a concern until you begin to miss multiple months, otherwise it can be a very normal thing-- even if it's never happened before.