Hello,
Thanks for posting your query at DoctorSpring.com
You have had consistently negative pregnancy tests, so I do not think you could be pregnant.
Such menstrual irregularities are common around 45.
These could be peri menopausal changes, or simply, an irregular period, that happens once in a while.
I would suggest you to wait it out.
Chart your menstrual cycles in the form of a menstrual diary.
If the irregularity persists, have an OB - GYN evaluation to confirm if this is indeed perimenopause or something like endometrial hyperplasia ( thickening of the lining of the uterus ) that can cause irregular and delayed cycles.
Then you should have an internal exam, a Pap smear, a pelvic ultrasound scan and hormone levels to look for perimenopause ( FSH, LH, Serum estradiol ).
Right now, just wait it out, and let me know how it pans out over the course of the next few days.
All the best
Please feel free to discuss further.

Okay.
Get the workup done as outlined, these might be perimenopausal transient hormonal disturbances.
Nothing much to worry about.