Thanks for your query.
Firstly after so many negative pregnancy
tests, and after an examination by a gynecologist, you are definitely not pregnant.
So please dont worry about that.
As for the rest of you rsymptoms, they sound like pre menstrual symptoms. Probably your period is just due in a few days.
Delay in cycles for so long could be due to thyroid hormone imbalance
, stress , anxiety
, emotional upheavals, rapid fluctuations in weight or due to some pelvic pathology, but that has been ruled out in your case by ultrasound
please ask for gynecologist to completely evaluate you for the remaining reasons and then prescribe appropriate treatment.