Welcome to HCM.
You have missed period of 2 months with negative pregnancy
test.Your USG scan reveals collection of fluid in & out of uterus
(may be in POD).
Also you get period tonight after completed antibiotics.
There may be other causes for delayed period like thyroid disorder
,wt gain or loss,psychological upset,altered eating habit,stress
etc.So you should be concerned about that.
As you get your period today,you may not take Primolut-N now.
But you should have to take those after period over (for next cycle) to regularize your period at least 3-6 months according to direction of your doctor.
You avoid stress by regular deep breathing,take healthy diet and proper sleep.