Delayed period but HCG negative test

I’m 34 years old, hypothyroidal, taking levithyroxine everyday. TTC and I’m delayed by 4 days but hcg tests negative.

Usually I get regular cycles by 28 to 30 days. Have been trying for a year 😕 but haven’t delayed period. Have I taken the test early. It’s almost 18 days past ovulation!!