Help a man out. Gf is nearly 6 weeks late. Tests are saying she's not pregnant but we're scared. Are they always accurate?

Anonymous
My girlfriend last had her period mid December. Its now the 4th of February .

So that is pretty late. We done two tests last week that came back negative. Up until last week she insisted she definitely wasn't. She seemed annoyed last night and very quiet. She said she was scared but doesn't think she is.

Is there any other reason why it could be this late? She has been stressed a lot recently between work and her PHD she also took the morning after pill 3 weeks ago, which we know sometimes can effect it.
Should we see a doctor or try another test? Is there any other explaination that isn't pregnancy?
Updates
+1 y
Thanks, we've had a doctor's appointment booked for a few days now. Not until next week. I just wanted to get your opinions as the wait is killing me.
Help a man out. Gf is nearly 6 weeks late. Tests are saying she's not pregnant but we're scared. Are they always accurate?
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